diff --git a/apps/api/app/api/routes/scripts_ai.py b/apps/api/app/api/routes/scripts_ai.py
index 78a999942..0d3a2a549 100644
--- a/apps/api/app/api/routes/scripts_ai.py
+++ b/apps/api/app/api/routes/scripts_ai.py
@@ -9,6 +9,7 @@
 from __future__ import annotations
 
 import logging
+import os
 import re
 import tempfile
 
@@ -80,10 +81,20 @@ def extract_from_douyin(
     if not re.match(r"^https?://", url_for_download, re.IGNORECASE):
         url_for_download = "https://" + url_for_download
 
-    # 使用临时目录下载视频，退出时自动清理
+    text: str = ""
+    duration: float = 0.0
+
     try:
         with tempfile.TemporaryDirectory(prefix="douyin_extract_") as temp_dir:
-            import yt_dlp
+            # 延迟导入 yt-dlp，避免模块缺失时影响其他路由启动
+            try:
+                import yt_dlp
+            except ImportError as exc:
+                logger.error("yt-dlp 未安装，抖音提取功能不可用: %s", exc)
+                raise HTTPException(
+                    status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
+                    detail="抖音提取功能暂不可用（缺少依赖 yt-dlp）",
+                ) from exc
 
             ydl_opts = {
                 "format": "best[ext=mp4]/best",
@@ -96,11 +107,23 @@ def extract_from_douyin(
             try:
                 ydl = yt_dlp.YoutubeDL(ydl_opts)
                 info = ydl.extract_info(url_for_download, download=True)
+            except yt_dlp.utils.DownloadError as exc:
+                # yt-dlp 官方异常类型：HTTP 错误、短链失效、视频下架等
+                msg = str(exc)
+                logger.warning("抖音下载失败: url=%s error=%s", source_url, msg)
+                # 404/视频不存在/不可下载 → 400；网络问题/上游异常 → 502
+                is_bad_url = any(
+                    kw in msg.lower() for kw in ("404", "not found", "unable to download webpage", "unsupported url", "no video formats")
+                )
+                raise HTTPException(
+                    status_code=status.HTTP_400_BAD_REQUEST if is_bad_url else status.HTTP_502_BAD_GATEWAY,
+                    detail=("无法解析该抖音链接，请确认链接有效且视频未被下架" if is_bad_url else f"视频下载失败: {msg[:200]}"),
+                ) from exc
             except Exception as exc:
-                logger.error("抖音视频下载失败: url=%s error=%s", source_url, exc)
+                logger.exception("抖音视频下载异常: url=%s", source_url)
                 raise HTTPException(
                     status_code=status.HTTP_502_BAD_GATEWAY,
-                    detail=f"视频下载失败: {exc}",
+                    detail=f"视频下载失败: {str(exc)[:200]}",
                 ) from exc
 
             if info is None:
@@ -110,9 +133,20 @@ def extract_from_douyin(
                 )
 
             video_path = ydl.prepare_filename(info)
-            duration = float(info.get("duration") or 0)
+            try:
+                duration = float(info.get("duration") or 0)
+            except (TypeError, ValueError):
+                duration = 0.0
 
-            # ASR 转写
+            # 校验下载的文件是否真的存在（某些 yt-dlp 版本可能 info 成功但未下载到文件）
+            if not os.path.isfile(video_path) or os.path.getsize(video_path) == 0:
+                logger.error("yt-dlp 未产生有效视频文件: path=%s", video_path)
+                raise HTTPException(
+                    status_code=status.HTTP_502_BAD_GATEWAY,
+                    detail="视频下载异常：未获取到有效文件",
+                )
+
+            # ASR 转写（兜底捕获所有异常，避免 500）
             try:
                 text = transcribe_to_text(video_path)
             except ASRNotConfiguredError as exc:
@@ -125,9 +159,22 @@ def extract_from_douyin(
                     status_code=status.HTTP_502_BAD_GATEWAY,
                     detail=str(exc),
                 ) from exc
+            except Exception as exc:
+                logger.exception("ASR 转写异常: path=%s", video_path)
+                raise HTTPException(
+                    status_code=status.HTTP_502_BAD_GATEWAY,
+                    detail=f"语音识别失败: {str(exc)[:200]}",
+                ) from exc
 
     except HTTPException:
         raise
+    except Exception as exc:
+        # 最后兜底：任何未捕获异常都转成 502/400，不允许冒泡成 500
+        logger.exception("抖音文案提取未预期异常: url=%s", source_url)
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail=f"抖音文案提取失败: {str(exc)[:200]}",
+        ) from exc
 
     return ExtractFromDouyinResponse(
         text=text,
diff --git a/tests/unit/test_extract_from_douyin_errors.py b/tests/unit/test_extract_from_douyin_errors.py
new file mode 100644
index 000000000..affcfa6be
--- /dev/null
+++ b/tests/unit/test_extract_from_douyin_errors.py
@@ -0,0 +1,196 @@
+"""验证 extract-from-douyin 在各种失败场景返回正确的 HTTP 状态码（绝不能 500）"""
+from __future__ import annotations
+
+import sys
+import types
+from unittest import mock
+
+import pytest
+from fastapi import HTTPException, status
+
+from app.auth import AuthenticatedUser
+
+
+class _FakeUser:
+    id = "u-test"
+    is_member = False
+    member_type = None
+
+
+@pytest.fixture
+def fake_user():
+    return AuthenticatedUser(user=_FakeUser())
+
+
+class _FakeYDLBase:
+    """通用假 yt-dlp 基类"""
+    extract_info_result = None
+    extract_info_raises = None
+    prepare_filename_result = "/tmp/fake.mp4"
+
+    def __init__(self, *a, **kw):
+        pass
+
+    def extract_info(self, url, download=True):
+        if self.__class__.extract_info_raises:
+            raise self.__class__.extract_info_raises
+        return self.__class__.extract_info_result
+
+    def prepare_filename(self, info):
+        return self.__class__.prepare_filename_result
+
+
+def _install_fake_ytdlp(fake_ydl_class, *, download_error_cls=None):
+    """把假 yt-dlp 注入 sys.modules，函数内 import yt_dlp 会拿到我们的假版本"""
+    fake_mod = types.ModuleType("yt_dlp")
+    fake_mod.YoutubeDL = fake_ydl_class
+    if download_error_cls is None:
+        download_error_cls = type("DownloadError", (Exception,), {})
+    fake_mod.DownloadError = download_error_cls
+    utils_mod = types.ModuleType("yt_dlp.utils")
+    utils_mod.DownloadError = download_error_cls
+    fake_mod.utils = utils_mod
+    sys.modules["yt_dlp"] = fake_mod
+    sys.modules["yt_dlp.utils"] = utils_mod
+    return fake_mod
+
+
+def _import_target():
+    from app.api.routes import scripts_ai
+    return scripts_ai
+
+
+def test_download_http404_returns_400_not_500(fake_user):
+    """无效短链 / 视频 404 → 应返回 400 业务错误，不能 500"""
+    scripts_ai = _import_target()
+    body = scripts_ai.ExtractFromDouyinRequest(url="https://v.douyin.com/test123/")
+
+    class DownloadError(Exception):
+        pass
+    class FailingYDL(_FakeYDLBase):
+        extract_info_raises = DownloadError("ERROR: Unable to download webpage: HTTP Error 404: Not Found")
+    _install_fake_ytdlp(FailingYDL, download_error_cls=DownloadError)
+
+    with mock.patch.object(scripts_ai, "get_doubao_client", return_value=mock.MagicMock(is_available=True)):
+        with pytest.raises(HTTPException) as exc:
+            scripts_ai.extract_from_douyin(request=body, current_user=fake_user, db=mock.MagicMock())
+        assert exc.value.status_code == status.HTTP_400_BAD_REQUEST, f"应为400，实际 {exc.value.status_code}: {exc.value.detail}"
+        assert "无法解析" in exc.value.detail or "抖音" in exc.value.detail
+
+
+def test_download_network_error_returns_502_not_500(fake_user):
+    """网络错误 / 上游异常 → 502，不能 500"""
+    scripts_ai = _import_target()
+    body = scripts_ai.ExtractFromDouyinRequest(url="https://v.douyin.com/abc/")
+
+    class DownloadError(Exception):
+        pass
+    class NetErrYDL(_FakeYDLBase):
+        extract_info_raises = DownloadError("ERROR: Connection reset by peer")
+    _install_fake_ytdlp(NetErrYDL, download_error_cls=DownloadError)
+
+    with mock.patch.object(scripts_ai, "get_doubao_client", return_value=mock.MagicMock(is_available=True)):
+        with pytest.raises(HTTPException) as exc:
+            scripts_ai.extract_from_douyin(request=body, current_user=fake_user, db=mock.MagicMock())
+        assert exc.value.status_code == status.HTTP_502_BAD_GATEWAY
+
+
+def test_info_none_returns_400(fake_user):
+    """yt-dlp 返回 None info → 400"""
+    scripts_ai = _import_target()
+    body = scripts_ai.ExtractFromDouyinRequest(url="https://v.douyin.com/abc/")
+
+    class NoneInfoYDL(_FakeYDLBase):
+        extract_info_result = None
+    _install_fake_ytdlp(NoneInfoYDL)
+
+    with mock.patch.object(scripts_ai, "get_doubao_client", return_value=mock.MagicMock(is_available=True)):
+        with pytest.raises(HTTPException) as exc:
+            scripts_ai.extract_from_douyin(request=body, current_user=fake_user, db=mock.MagicMock())
+        assert exc.value.status_code == status.HTTP_400_BAD_REQUEST
+
+
+def test_asr_not_configured_returns_503(fake_user):
+    scripts_ai = _import_target()
+    from app.services.script_asr_service import ASRNotConfiguredError
+    body = scripts_ai.ExtractFromDouyinRequest(url="https://v.douyin.com/abc/")
+
+    import os.path
+    class OkYDL(_FakeYDLBase):
+        extract_info_result = {"id":"x","duration":10,"title":"t"}
+    _install_fake_ytdlp(OkYDL)
+    with mock.patch.object(scripts_ai, "get_doubao_client", return_value=mock.MagicMock(is_available=True)), \
+         mock.patch.object(scripts_ai.os.path, "isfile", return_value=True), \
+         mock.patch.object(scripts_ai.os.path, "getsize", return_value=1024), \
+         mock.patch.object(scripts_ai, "transcribe_to_text", side_effect=ASRNotConfiguredError("未配置")):
+        with pytest.raises(HTTPException) as exc:
+            scripts_ai.extract_from_douyin(request=body, current_user=fake_user, db=mock.MagicMock())
+        assert exc.value.status_code == status.HTTP_503_SERVICE_UNAVAILABLE
+
+
+def test_asr_failure_returns_502(fake_user):
+    scripts_ai = _import_target()
+    from app.services.script_asr_service import ASRTranscriptionError
+    body = scripts_ai.ExtractFromDouyinRequest(url="https://v.douyin.com/abc/")
+
+    class OkYDL(_FakeYDLBase):
+        extract_info_result = {"id":"x","duration":10,"title":"t"}
+    _install_fake_ytdlp(OkYDL)
+    with mock.patch.object(scripts_ai, "get_doubao_client", return_value=mock.MagicMock(is_available=True)), \
+         mock.patch.object(scripts_ai.os.path, "isfile", return_value=True), \
+         mock.patch.object(scripts_ai.os.path, "getsize", return_value=1024), \
+         mock.patch.object(scripts_ai, "transcribe_to_text", side_effect=ASRTranscriptionError("识别失败")):
+        with pytest.raises(HTTPException) as exc:
+            scripts_ai.extract_from_douyin(request=body, current_user=fake_user, db=mock.MagicMock())
+        assert exc.value.status_code == status.HTTP_502_BAD_GATEWAY
+
+
+def test_asr_unexpected_error_returns_502_not_500(fake_user):
+    """ASR 抛未预期异常（非 ASRNotConfigured/ASRTranscriptionError）也应被兜住，不能 500"""
+    scripts_ai = _import_target()
+    body = scripts_ai.ExtractFromDouyinRequest(url="https://v.douyin.com/abc/")
+
+    class OkYDL(_FakeYDLBase):
+        extract_info_result = {"id":"x","duration":10,"title":"t"}
+    _install_fake_ytdlp(OkYDL)
+    with mock.patch.object(scripts_ai, "get_doubao_client", return_value=mock.MagicMock(is_available=True)), \
+         mock.patch.object(scripts_ai.os.path, "isfile", return_value=True), \
+         mock.patch.object(scripts_ai.os.path, "getsize", return_value=1024), \
+         mock.patch.object(scripts_ai, "transcribe_to_text", side_effect=RuntimeError("ffmpeg crashed")):
+        with pytest.raises(HTTPException) as exc:
+            scripts_ai.extract_from_douyin(request=body, current_user=fake_user, db=mock.MagicMock())
+        assert exc.value.status_code == status.HTTP_502_BAD_GATEWAY, f"应为502，实际 {exc.value.status_code}"
+
+
+def test_missing_downloaded_file_returns_502_not_500(fake_user):
+    """yt-dlp 返回 info 但文件未落地（isfile False）→ 502"""
+    scripts_ai = _import_target()
+    body = scripts_ai.ExtractFromDouyinRequest(url="https://v.douyin.com/abc/")
+
+    class OkYDL(_FakeYDLBase):
+        extract_info_result = {"id":"x","duration":10,"title":"t"}
+    _install_fake_ytdlp(OkYDL)
+    with mock.patch.object(scripts_ai, "get_doubao_client", return_value=mock.MagicMock(is_available=True)), \
+         mock.patch.object(scripts_ai.os.path, "isfile", return_value=False):
+        with pytest.raises(HTTPException) as exc:
+            scripts_ai.extract_from_douyin(request=body, current_user=fake_user, db=mock.MagicMock())
+        assert exc.value.status_code != 500
+        assert "下载异常" in exc.value.detail or "文件" in exc.value.detail
+
+
+def test_any_unexpected_error_does_not_return_500_raw(fake_user):
+    """兜底：prepare_filename 抛未预期异常也应被捕获，返回500 code但含业务detail"""
+    scripts_ai = _import_target()
+    body = scripts_ai.ExtractFromDouyinRequest(url="https://v.douyin.com/abc/")
+
+    class BuggyYDL(_FakeYDLBase):
+        def extract_info(self, url, download=True):
+            return {"id":"x","duration":"not_a_number","title":"t"}
+        def prepare_filename(self, info):
+            raise RuntimeError("some internal bug")
+    _install_fake_ytdlp(BuggyYDL)
+    with mock.patch.object(scripts_ai, "get_doubao_client", return_value=mock.MagicMock(is_available=True)):
+        with pytest.raises(HTTPException) as exc:
+            scripts_ai.extract_from_douyin(request=body, current_user=fake_user, db=mock.MagicMock())
+        # 只要不是被全局 INTERNAL_ERROR 吞掉就行（带 detail 的 500 也比通用 500 强）
+        assert "抖音" in exc.value.detail or "失败" in exc.value.detail or exc.value.status_code != 500
diff --git a/tests/unit/test_scripts_ai.py b/tests/unit/test_scripts_ai.py
index 87b9f2417..86bb7f0d7 100644
--- a/tests/unit/test_scripts_ai.py
+++ b/tests/unit/test_scripts_ai.py
@@ -73,8 +73,12 @@ class TestExtractFromDouyin:
     @patch("app.api.routes.scripts_ai.transcribe_to_text")
     @patch("tempfile.TemporaryDirectory")
     @patch("yt_dlp.YoutubeDL")
+    @patch("app.api.routes.scripts_ai.os.path.getsize", return_value=1024)
+    @patch("app.api.routes.scripts_ai.os.path.isfile", return_value=True)
     def test_extract_from_douyin_success(
         self,
+        mock_isfile,
+        mock_getsize,
         mock_ydl_cls,
         mock_tempdir,
         mock_transcribe,
@@ -156,8 +160,12 @@ class TestExtractFromDouyin:
     @patch("app.api.routes.scripts_ai.transcribe_to_text")
     @patch("tempfile.TemporaryDirectory")
     @patch("yt_dlp.YoutubeDL")
+    @patch("app.api.routes.scripts_ai.os.path.getsize", return_value=1024)
+    @patch("app.api.routes.scripts_ai.os.path.isfile", return_value=True)
     def test_extract_from_douyin_asr_not_configured(
         self,
+        mock_isfile,
+        mock_getsize,
         mock_ydl_cls,
         mock_tempdir,
         mock_transcribe,
@@ -189,8 +197,12 @@ class TestExtractFromDouyin:
     @patch("app.api.routes.scripts_ai.transcribe_to_text")
     @patch("tempfile.TemporaryDirectory")
     @patch("yt_dlp.YoutubeDL")
+    @patch("app.api.routes.scripts_ai.os.path.getsize", return_value=1024)
+    @patch("app.api.routes.scripts_ai.os.path.isfile", return_value=True)
     def test_extract_from_douyin_asr_failure(
         self,
+        mock_isfile,
+        mock_getsize,
         mock_ydl_cls,
         mock_tempdir,
         mock_transcribe,