diff --git a/packages/adapters/in_memory/asset_library_repository.py b/packages/adapters/in_memory/asset_library_repository.py
index 361938881..97b7012af 100644
--- a/packages/adapters/in_memory/asset_library_repository.py
+++ b/packages/adapters/in_memory/asset_library_repository.py
@@ -16,6 +16,9 @@ class InMemoryAssetLibraryRepository:
     def get(self, library_id: str) -> AssetLibrary | None:
         return self._libraries.get(library_id)
 
+    def find_by_id(self, library_id: str) -> AssetLibrary | None:
+        return self.get(library_id)
+
     def find_by_project(self, project_id: str, kind: AssetLibraryKind | None = None) -> list[AssetLibrary]:
         items = [library for library in self._libraries.values() if library.project_id == project_id]
         if kind is not None:
diff --git a/tests/unit/test_asset_library_delete.py b/tests/unit/test_asset_library_delete.py
new file mode 100644
index 000000000..648dcafa4
--- /dev/null
+++ b/tests/unit/test_asset_library_delete.py
@@ -0,0 +1,254 @@
+"""
+DELETE /asset-libraries/{library_id} 单元测试
+
+覆盖：
+- 正常删除空素材库（204）
+- 删除含素材的库（同时删除库内素材）
+- 素材库不存在（404）
+- 无权限访问（403）
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+from pathlib import Path
+from unittest.mock import MagicMock
+
+os.environ.setdefault("JWT_SECRET_KEY", "unit-test-secret-key-for-testing")
+os.environ.setdefault("DATABASE_URL", "sqlite:///test.db")
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[2] / "apps" / "api"))
+
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+from packages.adapters.in_memory.asset_library_repository import InMemoryAssetLibraryRepository
+from packages.adapters.in_memory.asset_repository import InMemoryAssetRepository
+from packages.domain import Asset, AssetLibrary, AssetLibraryKind, AssetStatus
+
+# ---------------------------------------------------------------------------
+# Stub Project Repository
+# ---------------------------------------------------------------------------
+
+
+class StubProject:
+    """最小化 Project stub，支持 can_access"""
+
+    def __init__(self, project_id: str, owner_id: str):
+        self.id = project_id
+        self._owner_id = owner_id
+
+    def can_access(self, user_id: str) -> bool:
+        return user_id == self._owner_id
+
+
+class StubProjectRepository:
+    def __init__(self, projects: dict[str, StubProject] | None = None):
+        self._projects = projects or {}
+
+    def find_by_id(self, project_id: str):
+        return self._projects.get(project_id)
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+def _make_auth_user(user_id: str = "user-001"):
+    from app.auth import AuthenticatedUser
+
+    from packages.domain.entities import User
+
+    user = User(id=user_id, email="test@example.com", display_name="测试用户")
+    return AuthenticatedUser(user=user)
+
+
+def _create_test_app(
+    library_repo: InMemoryAssetLibraryRepository,
+    asset_repo: InMemoryAssetRepository,
+    project_repo: StubProjectRepository,
+    user_id: str = "user-001",
+):
+    from app.api.routes import asset_libraries as module
+    from app.api.routes.asset_libraries import router
+
+    app = FastAPI()
+    app.include_router(router, prefix="/api/v1/asset-libraries")
+
+    app.dependency_overrides[module.get_current_user] = lambda: _make_auth_user(user_id)
+    app.dependency_overrides[module.get_asset_library_repository] = lambda: library_repo
+    app.dependency_overrides[module.get_asset_repository] = lambda: asset_repo
+    app.dependency_overrides[module.get_project_repository] = lambda: project_repo
+
+    return app
+
+
+# ---------------------------------------------------------------------------
+# Tests
+# ---------------------------------------------------------------------------
+
+
+class TestDeleteAssetLibrary:
+    """DELETE /asset-libraries/{library_id} 测试"""
+
+    def test_delete_empty_library(self):
+        """删除空素材库 → 204"""
+        from datetime import datetime, timezone
+
+        lib_repo = InMemoryAssetLibraryRepository()
+        asset_repo = InMemoryAssetRepository()
+        proj_repo = StubProjectRepository({"proj-1": StubProject("proj-1", "user-001")})
+
+        now = datetime.now(timezone.utc)
+        library = AssetLibrary(
+            id="lib-1",
+            project_id="proj-1",
+            name="视频素材库",
+            kind=AssetLibraryKind.VIDEO,
+            asset_count=0,
+            total_size=0,
+            created_at=now,
+            updated_at=now,
+        )
+        lib_repo.create(library)
+
+        app = _create_test_app(lib_repo, asset_repo, proj_repo)
+        client = TestClient(app)
+
+        response = client.delete("/api/v1/asset-libraries/lib-1")
+        assert response.status_code == 204
+
+        # 验证库已删除
+        assert lib_repo.find_by_id("lib-1") is None
+
+    def test_delete_library_with_assets(self):
+        """删除含素材的库 → 库和素材都被删除"""
+        from datetime import datetime, timezone
+
+        lib_repo = InMemoryAssetLibraryRepository()
+        asset_repo = InMemoryAssetRepository()
+        proj_repo = StubProjectRepository({"proj-1": StubProject("proj-1", "user-001")})
+
+        now = datetime.now(timezone.utc)
+        library = AssetLibrary(
+            id="lib-1",
+            project_id="proj-1",
+            name="视频素材库",
+            kind=AssetLibraryKind.VIDEO,
+            asset_count=3,
+            total_size=1000,
+            created_at=now,
+            updated_at=now,
+        )
+        lib_repo.create(library)
+
+        # 创建 3 个素材
+        for i in range(3):
+            asset = Asset.create(
+                project_id="proj-1",
+                library_id="lib-1",
+                name=f"video_{i}.mp4",
+                storage_key=f"uploads/video_{i}.mp4",
+                mime_type="video/mp4",
+                status=AssetStatus.READY,
+            )
+            asset_repo.create(asset)
+
+        # 创建一个不属于该库的素材（不应被删除）
+        other_asset = Asset.create(
+            project_id="proj-1",
+            library_id="lib-other",
+            name="other.mp4",
+            storage_key="uploads/other.mp4",
+            mime_type="video/mp4",
+            status=AssetStatus.READY,
+        )
+        asset_repo.create(other_asset)
+
+        app = _create_test_app(lib_repo, asset_repo, proj_repo)
+        client = TestClient(app)
+
+        response = client.delete("/api/v1/asset-libraries/lib-1")
+        assert response.status_code == 204
+
+        # 库已删除
+        assert lib_repo.find_by_id("lib-1") is None
+        # 库内素材已删除
+        assert asset_repo.find_by_library("lib-1") == []
+        # 其他素材未受影响
+        assert asset_repo.get(other_asset.id) is not None
+
+    def test_delete_nonexistent_library(self):
+        """删除不存在的素材库 → 404"""
+        lib_repo = InMemoryAssetLibraryRepository()
+        asset_repo = InMemoryAssetRepository()
+        proj_repo = StubProjectRepository({"proj-1": StubProject("proj-1", "user-001")})
+
+        app = _create_test_app(lib_repo, asset_repo, proj_repo)
+        client = TestClient(app)
+
+        response = client.delete("/api/v1/asset-libraries/nonexistent-id")
+        assert response.status_code == 404
+        assert "素材库不存在" in response.json()["detail"]
+
+    def test_delete_library_access_denied(self):
+        """无权限用户删除素材库 → 403"""
+        from datetime import datetime, timezone
+
+        lib_repo = InMemoryAssetLibraryRepository()
+        asset_repo = InMemoryAssetRepository()
+        # 项目属于 user-002，当前用户是 user-001
+        proj_repo = StubProjectRepository({"proj-1": StubProject("proj-1", "user-002")})
+
+        now = datetime.now(timezone.utc)
+        library = AssetLibrary(
+            id="lib-1",
+            project_id="proj-1",
+            name="视频素材库",
+            kind=AssetLibraryKind.VIDEO,
+            asset_count=0,
+            total_size=0,
+            created_at=now,
+            updated_at=now,
+        )
+        lib_repo.create(library)
+
+        app = _create_test_app(lib_repo, asset_repo, proj_repo, user_id="user-001")
+        client = TestClient(app)
+
+        response = client.delete("/api/v1/asset-libraries/lib-1")
+        assert response.status_code == 403
+        assert "Access denied" in response.json()["detail"]
+
+        # 库未被删除
+        assert lib_repo.find_by_id("lib-1") is not None
+
+    def test_delete_library_project_not_found(self):
+        """素材库所属项目不存在 → 404"""
+        from datetime import datetime, timezone
+
+        lib_repo = InMemoryAssetLibraryRepository()
+        asset_repo = InMemoryAssetRepository()
+        # 空的项目仓库，找不到项目
+        proj_repo = StubProjectRepository({})
+
+        now = datetime.now(timezone.utc)
+        library = AssetLibrary(
+            id="lib-1",
+            project_id="proj-missing",
+            name="视频素材库",
+            kind=AssetLibraryKind.VIDEO,
+            asset_count=0,
+            total_size=0,
+            created_at=now,
+            updated_at=now,
+        )
+        lib_repo.create(library)
+
+        app = _create_test_app(lib_repo, asset_repo, proj_repo)
+        client = TestClient(app)
+
+        response = client.delete("/api/v1/asset-libraries/lib-1")
+        assert response.status_code == 404