diff --git a/judge_dispatcher/migrations/0005_auto_20160519_1627.py b/judge_dispatcher/migrations/0005_auto_20160519_1627.py
new file mode 100644
index 00000000..280ce659
--- /dev/null
+++ b/judge_dispatcher/migrations/0005_auto_20160519_1627.py
@@ -0,0 +1,32 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.5 on 2016-05-19 08:27
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('judge_dispatcher', '0004_auto_20160407_1816'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='judgeserver',
+            name='left_instance_number',
+        ),
+        migrations.RemoveField(
+            model_name='judgeserver',
+            name='lock',
+        ),
+        migrations.RemoveField(
+            model_name='judgeserver',
+            name='workload',
+        ),
+        migrations.AddField(
+            model_name='judgeserver',
+            name='used_instance_number',
+            field=models.IntegerField(default=0),
+        ),
+    ]
diff --git a/judge_dispatcher/models.py b/judge_dispatcher/models.py
index 7305eb26..50b9c08d 100644
--- a/judge_dispatcher/models.py
+++ b/judge_dispatcher/models.py
@@ -8,11 +8,8 @@ class JudgeServer(models.Model):
     port = models.IntegerField()
     # 这个服务器最大可能运行的判题实例数量
     max_instance_number = models.IntegerField()
-    left_instance_number = models.IntegerField()
-    workload = models.IntegerField(default=0)
+    used_instance_number = models.IntegerField(default=0)
     token = models.CharField(max_length=30)
-    # 进行测试用例同步的时候加锁
-    lock = models.BooleanField(default=False)
     # status 为 false 的时候代表不使用这个服务器
     status = models.BooleanField(default=True)
     create_time = models.DateTimeField(auto_now_add=True, blank=True, null=True)
diff --git a/judge_dispatcher/tasks.py b/judge_dispatcher/tasks.py
index 32b24a08..6f57abcf 100644
--- a/judge_dispatcher/tasks.py
+++ b/judge_dispatcher/tasks.py
@@ -4,6 +4,7 @@ import logging
 import time
 
 from django.db import transaction
+from django.db.models import F
 
 from rpc_client import TimeoutServerProxy
 
@@ -39,11 +40,10 @@ class JudgeDispatcher(object):
 
     def choose_judge_server(self):
         with transaction.atomic():
-            servers = JudgeServer.objects.select_for_update().filter(workload__lt=100, lock=False, status=True).order_by("-workload")
+            servers = JudgeServer.objects.select_for_update().filter(used_instance_number__lt=F("max_instance_number"), status=True).order_by("max_instance_number")
             if servers.exists():
                 server = servers.first()
-                server.left_instance_number -= 1
-                server.workload = 100 - int(float(server.left_instance_number) / server.max_instance_number * 100)
+                server.used_instance_number = F("used_instance_number") + 1
                 server.save()
                 return server
 
@@ -51,8 +51,7 @@ class JudgeDispatcher(object):
         with transaction.atomic():
             # 使用原子操作, 同时因为use和release中间间隔了判题过程,需要重新查询一下
             server = JudgeServer.objects.select_for_update().get(id=judge_server_id)
-            server.left_instance_number += 1
-            server.workload = 100 - int(float(server.left_instance_number) / server.max_instance_number * 100)
+            server.used_instance_number = F("used_instance_number") - 1
             server.save()
 
     def judge(self):
diff --git a/template/src/admin/judges/judges.html b/template/src/admin/judges/judges.html
index 445b6ca2..2319d359 100644
--- a/template/src/admin/judges/judges.html
+++ b/template/src/admin/judges/judges.html
@@ -14,7 +14,7 @@
             <td>{{ el.id }}</td>
             <td>{{ el.name }}</td>
             <td>{{ el.max_instance_number }}</td>
-            <td>{{ el.workload }}</td>
+            <td>{{ el.used_instance_number / el.max_instance_number * 100 }}%</td>
             <td>{{ el.create_time|date("yyyy-MM-dd HH:mm:ss")}}</td>
             <td ms-text="el.status?'启用':'停用'"></td>
             <td>