diff --git a/app/services/documentary/frame_analysis_service.py b/app/services/documentary/frame_analysis_service.py
index 9cefda9..2813e9b 100644
--- a/app/services/documentary/frame_analysis_service.py
+++ b/app/services/documentary/frame_analysis_service.py
@@ -135,7 +135,13 @@ JSON 必须包含以下键：
                 }
             )
 
-        summary = payload["overall_activity_summary"]
+        raw_summary = payload.get("overall_activity_summary", "")
+        if isinstance(raw_summary, str):
+            summary = raw_summary
+        elif raw_summary is None:
+            summary = ""
+        else:
+            summary = str(raw_summary)
 
         return FrameBatchResult(
             batch_index=batch_index,
@@ -160,10 +166,4 @@ JSON 必须包含以下键：
                 f"{len(payload['frame_observations'])} < {expected_frame_count}"
             )
 
-        if "overall_activity_summary" not in payload:
-            return "Batch response must include overall_activity_summary"
-
-        if not isinstance(payload["overall_activity_summary"], str):
-            return "Batch response overall_activity_summary must be a string"
-
         return ""
diff --git a/tests/test_documentary_frame_analysis_service.py b/tests/test_documentary_frame_analysis_service.py
index edf585c..a444068 100644
--- a/tests/test_documentary_frame_analysis_service.py
+++ b/tests/test_documentary_frame_analysis_service.py
@@ -162,6 +162,31 @@ class DocumentaryFrameAnalysisServiceTests(unittest.TestCase):
         self.assertEqual("人物从房间走到街道", batch.overall_activity_summary)
         self.assertEqual("", batch.fallback_summary)
 
+    def test_parse_batch_preserves_frames_when_summary_is_missing(self):
+        service = DocumentaryFrameAnalysisService()
+        raw_response = """
+{
+  "frame_observations": [
+    {"observation": "第一帧画面"},
+    {"observation": "第二帧画面"}
+  ]
+}
+""".strip()
+
+        batch = service._parse_batch_response(
+            batch_index=2,
+            raw_response=raw_response,
+            frame_paths=[
+                "/tmp/keyframe_000000_000000000.jpg",
+                "/tmp/keyframe_000075_000003000.jpg",
+            ],
+            time_range="00:00:00,000-00:00:06,000",
+        )
+
+        self.assertEqual("success", batch.status)
+        self.assertEqual(2, len(batch.frame_observations))
+        self.assertEqual("", batch.overall_activity_summary)
+
     def test_cache_key_changes_when_interval_changes(self):
         service = DocumentaryFrameAnalysisService()