diff --git a/submission/migrations/0003_add_contest_create_time_idx.py b/submission/migrations/0003_add_contest_create_time_idx.py
new file mode 100644
index 0000000..fa87854
--- /dev/null
+++ b/submission/migrations/0003_add_contest_create_time_idx.py
@@ -0,0 +1,19 @@
+# Generated by Django 6.0 on 2026-03-09 13:06
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('contest', '0001_initial'),
+        ('problem', '0005_remove_spj_fields'),
+        ('submission', '0002_submission_user_create_time_idx'),
+    ]
+
+    operations = [
+        migrations.AddIndex(
+            model_name='submission',
+            index=models.Index(fields=['contest_id', '-create_time'], name='contest_create_time_idx'),
+        ),
+    ]
diff --git a/submission/models.py b/submission/models.py
index 7d7a6cb..c7ca45d 100644
--- a/submission/models.py
+++ b/submission/models.py
@@ -62,6 +62,9 @@ class Submission(models.Model):
             models.Index(
                 fields=["user_id", "create_time"], name="user_create_time_idx"
             ),
+            models.Index(
+                fields=["contest_id", "-create_time"], name="contest_create_time_idx"
+            ),
         ]
 
     def __str__(self):
diff --git a/submission/views/oj.py b/submission/views/oj.py
index 52d2fad..d23e28b 100644
--- a/submission/views/oj.py
+++ b/submission/views/oj.py
@@ -159,7 +159,7 @@ class SubmissionListAPI(APIView):
             return self.error("Parameter error")
 
         submissions = Submission.objects.filter(contest_id__isnull=True).select_related(
-            "problem", "problem__created_by"
+            "problem"
         ).order_by("-create_time")
         problem_id = request.GET.get("problem_id")
         myself = request.GET.get("myself")
@@ -207,7 +207,7 @@ class ContestSubmissionListAPI(APIView):
 
         contest = self.contest
         submissions = Submission.objects.filter(contest_id=contest.id).select_related(
-            "problem", "problem__created_by"
+            "problem", "contest"
         ).order_by("-create_time")
         problem_id = request.GET.get("problem_id")
         myself = request.GET.get("myself")