diff --git a/test_server/examtest/migrations/0024_auto_20200402_2353.py b/test_server/examtest/migrations/0024_auto_20200402_2353.py
new file mode 100644
index 0000000..a71fbaf
--- /dev/null
+++ b/test_server/examtest/migrations/0024_auto_20200402_2353.py
@@ -0,0 +1,24 @@
+# Generated by Django 3.0.4 on 2020-04-02 15:53
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('examtest', '0023_auto_20200402_2346'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='examtest',
+            name='paper',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, to='examtest.Paper', verbose_name='所用试卷'),
+        ),
+        migrations.AlterField(
+            model_name='examtest',
+            name='workscope',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, to='examtest.WorkScope', verbose_name='工作类别'),
+        ),
+    ]
diff --git a/test_server/examtest/models.py b/test_server/examtest/models.py
index 460ea9e..eeb637a 100644
--- a/test_server/examtest/models.py
+++ b/test_server/examtest/models.py
@@ -17,8 +17,8 @@ class ExamTest(CommonModel):
     name = models.CharField(max_length=200, verbose_name='名称')
     type = models.CharField(max_length=50, default='自助模考',choices = type_choices, verbose_name='考试类型')
     limit = models.IntegerField(default=0, verbose_name='限时(分钟)')
-    workscope = models.ForeignKey(WorkScope, on_delete=models.CASCADE, verbose_name='工作类别', null=True, blank=True)
-    paper = models.ForeignKey(Paper, on_delete=models.CASCADE, verbose_name='所用试卷', null=True, blank=True)
+    workscope = models.ForeignKey(WorkScope, on_delete=models.SET_NULL, verbose_name='工作类别', null=True, blank=True)
+    paper = models.ForeignKey(Paper, on_delete=models.SET_NULL, verbose_name='所用试卷', null=True, blank=True)
     consumer = models.ForeignKey(Consumer, on_delete=models.CASCADE, verbose_name='模考人')
     total_score = models.FloatField(default=0, verbose_name='总分')
     score = models.FloatField(default=0, verbose_name='得分')