diff --git a/skywalking-sniffer/skywalking-agent/src/main/java/com/a/eye/skywalking/agent/SkyWalkingAgent.java b/skywalking-sniffer/skywalking-agent/src/main/java/com/a/eye/skywalking/agent/SkyWalkingAgent.java
index 6a8df9340f0fdff0a7ab6a53b635b93542e30135..173ca6d4c2ea73dcbb42308befe0669e4d75f201 100644
--- a/skywalking-sniffer/skywalking-agent/src/main/java/com/a/eye/skywalking/agent/SkyWalkingAgent.java
+++ b/skywalking-sniffer/skywalking-agent/src/main/java/com/a/eye/skywalking/agent/SkyWalkingAgent.java
@@ -26,8 +26,8 @@ import static net.bytebuddy.matcher.ElementMatchers.isInterface;
 import static net.bytebuddy.matcher.ElementMatchers.not;
 
 /**
- * The main entrance of sky-waking agent.
- * It bases on javaagent mechanism.
+ * The main entrance of sky-waking agent,
+ * based on javaagent mechanism.
  *
  * @author wusheng
  */
diff --git a/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/conf/Constants.java b/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/conf/Constants.java
index 8751a1be483efe8e5c1ab422866df54a2c99c29b..4e5dbcb46f506573f9d47c0f42f2f9cf4df8b4ea 100644
--- a/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/conf/Constants.java
+++ b/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/conf/Constants.java
@@ -7,5 +7,5 @@ public class Constants {
 	 * This is the version, which will be the first segment of traceid.
 	 * Ref {@link TraceIdGenerator#generate()}
 	 */
-	public static String SDK_VERSION = "302017";
+	public final static String SDK_VERSION = "302017";
 }
diff --git a/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/conf/SnifferConfigInitializer.java b/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/conf/SnifferConfigInitializer.java
index 1a267fa78ab8a29ad0d551cff936700e5f7958c4..dd37d05a670c2012c5f42e6a2ca018a7cbbdebb7 100644
--- a/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/conf/SnifferConfigInitializer.java
+++ b/skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/conf/SnifferConfigInitializer.java
@@ -11,7 +11,7 @@ import java.io.InputStream;
 import java.util.Properties;
 
 public class SnifferConfigInitializer {
-	private static ILog logger = LogManager.getLogger(SnifferConfigInitializer.class);
+    private static ILog logger = LogManager.getLogger(SnifferConfigInitializer.class);
 
     public static void initialize() {
         InputStream configFileStream;
@@ -32,24 +32,34 @@ public class SnifferConfigInitializer {
                 logger.error("Failed to read the config file, sky-walking api run in default config.", e);
             }
         }
-        Config.SkyWalking.USERNAME = System.getProperty("username");
-        Config.SkyWalking.APPLICATION_CODE = System.getProperty("applicationCode");
-        Config.SkyWalking.SERVERS = System.getProperty("servers");
 
-        if(StringUtil.isEmpty(Config.SkyWalking.USERNAME)){
+        String username = System.getProperty("username");
+        if (!StringUtil.isEmpty(username)) {
+            Config.SkyWalking.USERNAME = username;
+        }
+        String applicationCode = System.getProperty("applicationCode");
+        if (!StringUtil.isEmpty(applicationCode)) {
+            Config.SkyWalking.APPLICATION_CODE = applicationCode;
+        }
+        String servers = System.getProperty("servers");
+        if(!StringUtil.isEmpty(servers)) {
+            Config.SkyWalking.SERVERS = servers;
+        }
+
+        if (StringUtil.isEmpty(Config.SkyWalking.USERNAME)) {
             throw new ExceptionInInitializerError("'-Dusername=' is missing.");
         }
-        if(StringUtil.isEmpty(Config.SkyWalking.APPLICATION_CODE)){
+        if (StringUtil.isEmpty(Config.SkyWalking.APPLICATION_CODE)) {
             throw new ExceptionInInitializerError("'-DapplicationCode=' is missing.");
         }
-        if(StringUtil.isEmpty(Config.SkyWalking.SERVERS)){
+        if (StringUtil.isEmpty(Config.SkyWalking.SERVERS)) {
             throw new ExceptionInInitializerError("'-Dservers=' is missing.");
         }
     }
 
     private static InputStream fetchAuthFileInputStream() {
         try {
-            return new FileInputStream(Config.SkyWalking.AGENT_BASE_PATH + File.separator + "/sky-walking.config");
+            return new FileInputStream(Config.SkyWalking.AGENT_BASE_PATH + File.separator + "sky-walking.config");
         } catch (Exception e) {
             logger.warn("sky-walking.config is missing, use default config.");
             return null;
diff --git a/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/conf/ConstantsTest.java b/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/conf/ConstantsTest.java
new file mode 100644
index 0000000000000000000000000000000000000000..8f9f7f314b96fec95f6b8366a50f7f097bc4eb43
--- /dev/null
+++ b/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/conf/ConstantsTest.java
@@ -0,0 +1,14 @@
+package com.a.eye.skywalking.api.conf;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Created by wusheng on 2017/2/28.
+ */
+public class ConstantsTest {
+    @Test
+    public void testSDKVersion(){
+        Assert.assertEquals("302017", Constants.SDK_VERSION);
+    }
+}
diff --git a/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/conf/SnifferConfigInitializerTest.java b/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/conf/SnifferConfigInitializerTest.java
new file mode 100644
index 0000000000000000000000000000000000000000..3c32e45ecfa55414c5edf5192a048ef715996150
--- /dev/null
+++ b/skywalking-sniffer/skywalking-api/src/test/java/com/a/eye/skywalking/api/conf/SnifferConfigInitializerTest.java
@@ -0,0 +1,38 @@
+package com.a.eye.skywalking.api.conf;
+
+import org.junit.AfterClass;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * @author wusheng
+ */
+public class SnifferConfigInitializerTest {
+
+    @Test
+    public void testInitialize(){
+        Config.SkyWalking.IS_PREMAIN_MODE = false;
+        SnifferConfigInitializer.initialize();
+
+        Assert.assertEquals("testUser", Config.SkyWalking.USERNAME);
+        Assert.assertEquals("crmApp", Config.SkyWalking.APPLICATION_CODE);
+        Assert.assertEquals("127.0.0.1:8080", Config.SkyWalking.SERVERS);
+
+        Assert.assertNotNull(Config.Disruptor.BUFFER_SIZE);
+        Assert.assertNotNull(Config.Logging.LOG_DIR_NAME);
+        Assert.assertNotNull(Config.Logging.LOG_FILE_NAME);
+        Assert.assertNotNull(Config.Logging.MAX_LOG_FILE_LENGTH);
+        Assert.assertNotNull(Config.Logging.SYSTEM_ERROR_LOG_FILE_NAME);
+    }
+
+    @Test(expected = ExceptionInInitializerError.class)
+    public void testErrorInitialize(){
+        Config.SkyWalking.IS_PREMAIN_MODE = true;
+        SnifferConfigInitializer.initialize();
+    }
+
+    @AfterClass
+    public static void reset(){
+        Config.SkyWalking.IS_PREMAIN_MODE = false;
+    }
+}
diff --git a/skywalking-sniffer/skywalking-api/src/test/resources/sky-walking.config b/skywalking-sniffer/skywalking-api/src/test/resources/sky-walking.config
new file mode 100644
index 0000000000000000000000000000000000000000..8c35dada7d1d6e6a5232b712c835b86be33d7251
--- /dev/null
+++ b/skywalking-sniffer/skywalking-api/src/test/resources/sky-walking.config
@@ -0,0 +1,3 @@
+skywalking.username = testUser
+skywalking.application_code = crmApp
+skywalking.servers = 127.0.0.1:8080