diff --git a/apps/qm/serializers.py b/apps/qm/serializers.py
index 1868b840..98f13d2a 100644
--- a/apps/qm/serializers.py
+++ b/apps/qm/serializers.py
@@ -371,7 +371,8 @@ class FtestProcessSerializer(CustomModelSerializer):
                     else:
                         item2["is_main"] = False
                 FtestDefect.objects.create(ftest=instance, **item2)
-            instance.defect_main = defect_main
+            if not is_ok:
+                instance.defect_main = defect_main
             instance.is_ok = is_ok
             instance.save()
         return instance
@@ -412,7 +413,8 @@ class FtestProcessSerializer(CustomModelSerializer):
                     else:
                         ins.is_main = False
                     ins.save()
-            instance.defect_main = defect_main
+            if not is_ok:
+                instance.defect_main = defect_main
             instance.is_ok = is_ok
             instance.save()
         return instance
\ No newline at end of file