diff --git a/apps/api/app/api/routes/generation_preview.py b/apps/api/app/api/routes/generation_preview.py
index eeebe3ed1..f27d26d6e 100755
--- a/apps/api/app/api/routes/generation_preview.py
+++ b/apps/api/app/api/routes/generation_preview.py
@@ -74,7 +74,14 @@ def _sign_video_url(raw_url: str) -> str:
     try:
         storage = get_storage_service()
         signed = storage.get_download_url(raw_url, expires_seconds=7200)
-        return signed or raw_url
+        # 如果返回的 URL 与原始 URL 完全不同且不是签名 URL（说明 bucket 未配置），
+        # 降级返回原始 URL
+        if signed and signed != raw_url:
+            return signed
+        if signed == raw_url:
+            return raw_url
+        # signed 为空或与 raw_url 无关，返回原始
+        return raw_url
     except Exception:
         logger.warning("[预览] URL签名失败，降级返回原始URL: %s", raw_url[:100], exc_info=True)
         return raw_url