diff --git a/apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/plugin/PluginDefine.java b/apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/plugin/PluginDefine.java
index 5ccd13b70..307139574 100644
--- a/apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/plugin/PluginDefine.java
+++ b/apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/plugin/PluginDefine.java
@@ -5,6 +5,7 @@ import org.skywalking.apm.agent.core.plugin.exception.IllegalPluginDefineExcepti
 import org.skywalking.apm.util.StringUtil;
 
 public class PluginDefine {
+    public static final String PLUGIN_OFF_PREFIX = "[OFF]";
     /**
      * Plugin name.
      */
@@ -38,17 +39,20 @@ public class PluginDefine {
 
         String pluginName = pluginDefine[0];
         String defineClass = pluginDefine[1];
-        if (pluginName.toUpperCase().startsWith("[OFF]")) {
-            return new PluginDefine(pluginName.substring(5), defineClass, State.OFF);
+        if (pluginName.toUpperCase().startsWith(PLUGIN_OFF_PREFIX)) {
+            return new PluginDefine(pluginName.substring(PLUGIN_OFF_PREFIX.length()), defineClass, State.OFF);
         } else {
             return new PluginDefine(pluginName, defineClass, State.ON);
         }
     }
 
     public boolean enable() {
-        return !Config.Plugin.DISABLED_PLUGINS.contains(name) || forceEnable();
+        return !forceDisable() || forceEnable();
     }
 
+    private boolean forceDisable() {
+        return state != State.ON || Config.Plugin.DISABLED_PLUGINS.contains(name);
+    }
 
     private boolean forceEnable() {
         return state == State.OFF && Config.Plugin.FORCE_ENABLE_PLUGINS.contains(name);
diff --git a/apm-sniffer/apm-agent-core/src/test/java/org/skywalking/apm/agent/core/plugin/PluginDefineTest.java b/apm-sniffer/apm-agent-core/src/test/java/org/skywalking/apm/agent/core/plugin/PluginDefineTest.java
new file mode 100644
index 000000000..1f0a69dd9
--- /dev/null
+++ b/apm-sniffer/apm-agent-core/src/test/java/org/skywalking/apm/agent/core/plugin/PluginDefineTest.java
@@ -0,0 +1,48 @@
+package org.skywalking.apm.agent.core.plugin;
+
+import org.junit.Test;
+import org.skywalking.apm.agent.core.conf.Config;
+import org.skywalking.apm.agent.core.plugin.exception.IllegalPluginDefineException;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class PluginDefineTest {
+
+    private static final String TEST_PLUGIN = "test_plugin";
+    private static final String TEST_DEFINE_CLASS = "test_define_class";
+
+    @Test(expected = IllegalPluginDefineException.class)
+    public void testIllegalPluginDefine() throws IllegalPluginDefineException {
+        PluginDefine.build("illegal_plugin_define");
+    }
+
+    @Test(expected = IllegalPluginDefineException.class)
+    public void testEmptyPluginDefine() throws IllegalPluginDefineException {
+        PluginDefine.build("");
+    }
+
+    @Test
+    public void testOffStatePlugin() throws IllegalPluginDefineException {
+        PluginDefine pluginDefine = PluginDefine.build(PluginDefine.PLUGIN_OFF_PREFIX + TEST_PLUGIN + "=" + TEST_DEFINE_CLASS);
+        assertFalse(pluginDefine.enable());
+        assertEquals(TEST_DEFINE_CLASS, pluginDefine.getDefineClass());
+    }
+
+    @Test
+    public void testDefaultStatePlugin() throws IllegalPluginDefineException {
+        PluginDefine pluginDefine = PluginDefine.build(TEST_PLUGIN + "=" + TEST_DEFINE_CLASS);
+        assertTrue(pluginDefine.enable());
+        assertEquals(TEST_DEFINE_CLASS, pluginDefine.getDefineClass());
+    }
+
+    @Test
+    public void testForceEnablePlugin() throws IllegalPluginDefineException {
+        Config.Plugin.FORCE_ENABLE_PLUGINS.add(TEST_PLUGIN);
+        PluginDefine pluginDefine = PluginDefine.build(PluginDefine.PLUGIN_OFF_PREFIX + TEST_PLUGIN + "=" + TEST_DEFINE_CLASS);
+        assertTrue(pluginDefine.enable());
+        assertEquals(TEST_DEFINE_CLASS, pluginDefine.getDefineClass());
+        Config.Plugin.FORCE_ENABLE_PLUGINS.clear();
+    }
+}