diff --git a/fam-core/src/fam_core/db_layer.py b/fam-core/src/fam_core/db_layer.py
index 7a633d1..856d591 100644
--- a/fam-core/src/fam_core/db_layer.py
+++ b/fam-core/src/fam_core/db_layer.py
@@ -175,6 +175,11 @@ def get_video_url_exists(video_path: str) -> bool:
 # monitor_events 操作
 # ============================================================
 
+def _dt_or_none(value):
+    """datetime 字段归一化: 空串/None → NULL（MariaDB 严格模式拒绝 '' 插入 DATETIME 列）"""
+    return value if value else None
+
+
 def insert_event(task_id: int, event_start_time: str, event_end_time: str,
                  camera_name: str, global_summary: str, entities_json: list,
                  compute_provider: list) -> int:
@@ -187,7 +192,7 @@ def insert_event(task_id: int, event_start_time: str, event_end_time: str,
                (task_id, event_start_time, event_end_time, camera_name,
                 global_summary, entities_json, compute_provider)
                VALUES (%s, %s, %s, %s, %s, %s, %s)""",
-            (task_id, event_start_time, event_end_time, camera_name,
+            (task_id, _dt_or_none(event_start_time), _dt_or_none(event_end_time), camera_name,
              global_summary, json.dumps(entities_json, ensure_ascii=False),
              json.dumps(compute_provider, ensure_ascii=False))
         )
@@ -214,7 +219,7 @@ def insert_event_detail(event_id: int, task_id: int, frame_index: int,
                (event_id, task_id, frame_index, frame_timestamp, camera_name,
                 person, action, clothing, is_attention_event, source_providers)
                VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s, %s)""",
-            (event_id, task_id, frame_index, frame_timestamp, camera_name,
+            (event_id, task_id, frame_index, _dt_or_none(frame_timestamp), camera_name,
              person, action, clothing, is_attention_event,
              json.dumps(source_providers, ensure_ascii=False))
         )