diff --git a/api/core/app/apps/advanced_chat/generate_task_pipeline.py b/api/core/app/apps/advanced_chat/generate_task_pipeline.py
index 3bf6c330db..baefca0c3f 100644
--- a/api/core/app/apps/advanced_chat/generate_task_pipeline.py
+++ b/api/core/app/apps/advanced_chat/generate_task_pipeline.py
@@ -684,7 +684,9 @@ class AdvancedChatAppGenerateTaskPipeline:
                 )
             elif isinstance(event, QueueMessageReplaceEvent):
                 # published by moderation
-                yield self._message_cycle_manager._message_replace_to_stream_response(answer=event.text)
+                yield self._message_cycle_manager._message_replace_to_stream_response(
+                    answer=event.text, reason=event.reason
+                )
             elif isinstance(event, QueueAdvancedChatMessageEndEvent):
                 if not graph_runtime_state:
                     raise ValueError("graph runtime state not initialized.")
@@ -695,7 +697,8 @@ class AdvancedChatAppGenerateTaskPipeline:
                 if output_moderation_answer:
                     self._task_state.answer = output_moderation_answer
                     yield self._message_cycle_manager._message_replace_to_stream_response(
-                        answer=output_moderation_answer
+                        answer=output_moderation_answer,
+                        reason=QueueMessageReplaceEvent.MessageReplaceReason.OUTPUT_MODERATION,
                     )
 
                 # Save message
diff --git a/api/core/app/entities/queue_entities.py b/api/core/app/entities/queue_entities.py
index 3702326406..7228020e9b 100644
--- a/api/core/app/entities/queue_entities.py
+++ b/api/core/app/entities/queue_entities.py
@@ -264,8 +264,16 @@ class QueueMessageReplaceEvent(AppQueueEvent):
     QueueMessageReplaceEvent entity
     """
 
+    class MessageReplaceReason(StrEnum):
+        """
+        Reason for message replace event
+        """
+
+        OUTPUT_MODERATION = "output_moderation"
+
     event: QueueEvent = QueueEvent.MESSAGE_REPLACE
     text: str
+    reason: str
 
 
 class QueueRetrieverResourcesEvent(AppQueueEvent):
diff --git a/api/core/app/entities/task_entities.py b/api/core/app/entities/task_entities.py
index f23ee1b9fd..817699bd20 100644
--- a/api/core/app/entities/task_entities.py
+++ b/api/core/app/entities/task_entities.py
@@ -148,6 +148,7 @@ class MessageReplaceStreamResponse(StreamResponse):
 
     event: StreamEvent = StreamEvent.MESSAGE_REPLACE
     answer: str
+    reason: str
 
 
 class AgentThoughtStreamResponse(StreamResponse):
diff --git a/api/core/app/task_pipeline/based_generate_task_pipeline.py b/api/core/app/task_pipeline/based_generate_task_pipeline.py
index a2e06d4e1f..5331c0cc94 100644
--- a/api/core/app/task_pipeline/based_generate_task_pipeline.py
+++ b/api/core/app/task_pipeline/based_generate_task_pipeline.py
@@ -126,12 +126,12 @@ class BasedGenerateTaskPipeline:
         if self._output_moderation_handler:
             self._output_moderation_handler.stop_thread()
 
-            completion = self._output_moderation_handler.moderation_completion(
+            completion, flagged = self._output_moderation_handler.moderation_completion(
                 completion=completion, public_event=False
             )
 
             self._output_moderation_handler = None
-
-            return completion
+            if flagged:
+                return completion
 
         return None
diff --git a/api/core/app/task_pipeline/message_cycle_manage.py b/api/core/app/task_pipeline/message_cycle_manage.py
index 6223b33b67..fde506639f 100644
--- a/api/core/app/task_pipeline/message_cycle_manage.py
+++ b/api/core/app/task_pipeline/message_cycle_manage.py
@@ -182,10 +182,12 @@ class MessageCycleManage:
             from_variable_selector=from_variable_selector,
         )
 
-    def _message_replace_to_stream_response(self, answer: str) -> MessageReplaceStreamResponse:
+    def _message_replace_to_stream_response(self, answer: str, reason: str = "") -> MessageReplaceStreamResponse:
         """
         Message replace to stream response.
         :param answer: answer
         :return:
         """
-        return MessageReplaceStreamResponse(task_id=self._application_generate_entity.task_id, answer=answer)
+        return MessageReplaceStreamResponse(
+            task_id=self._application_generate_entity.task_id, answer=answer, reason=reason
+        )
diff --git a/api/core/moderation/output_moderation.py b/api/core/moderation/output_moderation.py
index e595be126c..2ec315417f 100644
--- a/api/core/moderation/output_moderation.py
+++ b/api/core/moderation/output_moderation.py
@@ -46,14 +46,14 @@ class OutputModeration(BaseModel):
         if not self.thread:
             self.thread = self.start_thread()
 
-    def moderation_completion(self, completion: str, public_event: bool = False) -> str:
+    def moderation_completion(self, completion: str, public_event: bool = False) -> tuple[str, bool]:
         self.buffer = completion
         self.is_final_chunk = True
 
         result = self.moderation(tenant_id=self.tenant_id, app_id=self.app_id, moderation_buffer=completion)
 
         if not result or not result.flagged:
-            return completion
+            return completion, False
 
         if result.action == ModerationAction.DIRECT_OUTPUT:
             final_output = result.preset_response
@@ -61,9 +61,14 @@ class OutputModeration(BaseModel):
             final_output = result.text
 
         if public_event:
-            self.queue_manager.publish(QueueMessageReplaceEvent(text=final_output), PublishFrom.TASK_PIPELINE)
+            self.queue_manager.publish(
+                QueueMessageReplaceEvent(
+                    text=final_output, reason=QueueMessageReplaceEvent.MessageReplaceReason.OUTPUT_MODERATION
+                ),
+                PublishFrom.TASK_PIPELINE,
+            )
 
-        return final_output
+        return final_output, True
 
     def start_thread(self) -> threading.Thread:
         buffer_size = dify_config.MODERATION_BUFFER_SIZE
@@ -112,7 +117,12 @@ class OutputModeration(BaseModel):
 
                 # trigger replace event
                 if self.thread_running:
-                    self.queue_manager.publish(QueueMessageReplaceEvent(text=final_output), PublishFrom.TASK_PIPELINE)
+                    self.queue_manager.publish(
+                        QueueMessageReplaceEvent(
+                            text=final_output, reason=QueueMessageReplaceEvent.MessageReplaceReason.OUTPUT_MODERATION
+                        ),
+                        PublishFrom.TASK_PIPELINE,
+                    )
 
                 if result.action == ModerationAction.DIRECT_OUTPUT:
                     break