diff --git a/prompt/api.py b/prompt/api.py
index 1558583..628a9d8 100644
--- a/prompt/api.py
+++ b/prompt/api.py
@@ -109,7 +109,7 @@ def delete_message_pair(request, message_id: int):
     """
     asst_msg = get_object_or_404(Message, id=message_id, role="assistant")
 
-    if asst_msg.conversation.user != request.user:
+    if asst_msg.conversation.user != request.user and request.user.role != RoleChoices.SUPER:
         raise HttpError(403, "只能删除自己的消息")
 
     # Find the preceding user message
diff --git a/prompt/migrations/0006_message_submission_cascade_delete.py b/prompt/migrations/0006_message_submission_cascade_delete.py
new file mode 100644
index 0000000..65f434c
--- /dev/null
+++ b/prompt/migrations/0006_message_submission_cascade_delete.py
@@ -0,0 +1,20 @@
+# Generated by Django 6.0.1 on 2026-04-16 06:15
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('prompt', '0005_message_add_submission_fk'),
+        ('submission', '0010_remove_conversation_fk'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='message',
+            name='submission',
+            field=models.OneToOneField(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='source_message', to='submission.submission'),
+        ),
+    ]
diff --git a/prompt/models.py b/prompt/models.py
index c817e23..7d5b034 100644
--- a/prompt/models.py
+++ b/prompt/models.py
@@ -1,7 +1,5 @@
 import uuid
 from django.db import models
-from django.db.models.signals import pre_delete
-from django.dispatch import receiver
 from django_extensions.db.models import TimeStampedModel
 from account.models import User
 from task.models import Task
@@ -38,7 +36,7 @@ class Message(models.Model):
         "submission.Submission",
         null=True,
         blank=True,
-        on_delete=models.SET_NULL,
+        on_delete=models.CASCADE,
         related_name="source_message",
     )
 
@@ -47,10 +45,3 @@ class Message(models.Model):
 
     def __str__(self):
         return f"[{self.role}] {self.content[:50]}"
-
-
-@receiver(pre_delete, sender=Message)
-def delete_linked_submission(sender, instance, **kwargs):
-    if instance.submission_id:
-        from submission.models import Submission
-        Submission.objects.filter(id=instance.submission_id).delete()
diff --git a/submission/api.py b/submission/api.py
index 1558ac1..6ec9d45 100644
--- a/submission/api.py
+++ b/submission/api.py
@@ -39,6 +39,7 @@ def create_submission(request, payload: SubmissionIn):
     """
     task = get_object_or_404(Task, id=payload.task_id)
 
+    manual_asst_msg = None
     if payload.prompt:
         conversation = (
             Conversation.objects.filter(user=request.user, task=task)
@@ -53,7 +54,7 @@ def create_submission(request, payload: SubmissionIn):
         Message.objects.create(
             conversation=conversation, role="user", content=payload.prompt, source="manual"
         )
-        Message.objects.create(
+        manual_asst_msg = Message.objects.create(
             conversation=conversation,
             role="assistant",
             content="",
@@ -83,8 +84,11 @@ def create_submission(request, payload: SubmissionIn):
         js=payload.js,
     )
 
-    # Link assistant message if provided
-    if payload.message_id:
+    # Link assistant message to submission
+    if manual_asst_msg:
+        manual_asst_msg.submission = submission
+        manual_asst_msg.save(update_fields=["submission"])
+    elif payload.message_id:
         try:
             msg = Message.objects.get(
                 id=payload.message_id,
@@ -207,11 +211,12 @@ def clear_all_flags(request):
 @login_required
 def delete_submission(request, submission_id: UUID):
     submission = get_object_or_404(Submission, id=submission_id)
-    if submission.user != request.user:
+    if submission.user != request.user and request.user.role != RoleChoices.SUPER:
         raise HttpError(403, "只能删除自己的提交")
 
-    # Delete linked message pair if present
+    # 找到关联的助手消息，再找前一条用户消息
     asst_msg = Message.objects.filter(submission=submission).first()
+    user_msg = None
     if asst_msg:
         user_msg = (
             Message.objects.filter(
@@ -222,11 +227,12 @@ def delete_submission(request, submission_id: UUID):
             .order_by("-created")
             .first()
         )
-        if user_msg:
-            user_msg.delete()
-        asst_msg.delete()
 
-    submission.delete()
+    submission.delete()  # CASCADE 自动删除关联的 asst_msg
+
+    if user_msg:
+        user_msg.delete()
+
     return {"message": "删除成功"}