diff --git a/webmagic-core/src/main/java/us/codecraft/webmagic/Spider.java b/webmagic-core/src/main/java/us/codecraft/webmagic/Spider.java
index 2a8b78fb..a25fd024 100644
--- a/webmagic-core/src/main/java/us/codecraft/webmagic/Spider.java
+++ b/webmagic-core/src/main/java/us/codecraft/webmagic/Spider.java
@@ -58,6 +58,8 @@ public class Spider implements Runnable, Task {
 
     private ExecutorService executorService;
 
+    private int threadNum = 1;
+
     private AtomicInteger stat = new AtomicInteger(STAT_INIT);
 
     private final static int STAT_INIT = 0;
@@ -144,6 +146,10 @@ public class Spider implements Runnable, Task {
         if (downloader == null) {
             this.downloader = new HttpClientDownloader();
         }
+        if (pipelines.isEmpty()) {
+            pipelines.add(new ConsolePipeline());
+        }
+        downloader.setThread(threadNum);
     }
 
     @Override
@@ -158,9 +164,6 @@ public class Spider implements Runnable, Task {
             }
         }
         Request request = scheduler.poll(this);
-        if (pipelines.isEmpty()) {
-            pipelines.add(new ConsolePipeline());
-        }
         //singel thread
         if (executorService == null) {
             while (request != null) {
@@ -211,9 +214,9 @@ public class Spider implements Runnable, Task {
         }
     }
 
-    private void destroyEach(Object object){
+    private void destroyEach(Object object) {
         if (object instanceof Destroyable) {
-            ((Destroyable)object).destroy();
+            ((Destroyable) object).destroy();
         }
     }
 
@@ -267,12 +270,10 @@ public class Spider implements Runnable, Task {
      */
     public Spider thread(int threadNum) {
         checkIfNotRunning();
+        this.threadNum = threadNum;
         if (threadNum <= 0) {
             throw new IllegalArgumentException("threadNum should be more than one!");
         }
-        if (downloader==null || downloader instanceof HttpClientDownloader){
-            downloader = new HttpClientDownloader(threadNum);
-        }
         if (threadNum == 1) {
             return this;
         }
diff --git a/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/Downloader.java b/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/Downloader.java
index c431fc3b..9a7f59a3 100644
--- a/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/Downloader.java
+++ b/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/Downloader.java
@@ -6,9 +6,10 @@ import us.codecraft.webmagic.Task;
 
 /**
  * Downloader是webmagic下载页面的接口。webmagic默认使用了HttpComponent作为下载器，一般情况，你无需自己实现这个接口。<br>
+ *
  * @author code4crafter@gmail.com <br>
- * Date: 13-4-21
- * Time: 下午12:14
+ *         Date: 13-4-21
+ *         Time: 下午12:14
  */
 public interface Downloader {
 
@@ -20,4 +21,12 @@ public interface Downloader {
      * @return page
      */
     public Page download(Request request, Task task);
+
+    /**
+     * 设置线程数，多线程程序一般需要Downloader支持<br>
+     * 如果不考虑多线程的可以不实现这个方法<br>
+     *
+     * @param thread 线程数量
+     */
+    public void setThread(int thread);
 }
diff --git a/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/FileDownloader.java b/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/FileDownloader.java
index d22bf081..722a2eb7 100644
--- a/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/FileDownloader.java
+++ b/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/FileDownloader.java
@@ -67,6 +67,11 @@ public class FileDownloader implements Downloader {
         return page;
     }
 
+    @Override
+    public void setThread(int thread) {
+
+    }
+
     private String getHtml(BufferedReader bufferedReader) throws IOException {
         String line;
         StringBuilder htmlBuilder= new StringBuilder();
diff --git a/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/HttpClientDownloader.java b/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/HttpClientDownloader.java
index d7634198..7956cd1e 100644
--- a/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/HttpClientDownloader.java
+++ b/webmagic-core/src/main/java/us/codecraft/webmagic/downloader/HttpClientDownloader.java
@@ -32,14 +32,6 @@ public class HttpClientDownloader implements Downloader {
 
     private int poolSize;
 
-    public HttpClientDownloader(int poolSize) {
-        this.poolSize = poolSize;
-    }
-
-    public HttpClientDownloader() {
-        this(5);
-    }
-
     @Override
     public Page download(Request request, Task task) {
         Site site = task.getSite();
@@ -90,6 +82,11 @@ public class HttpClientDownloader implements Downloader {
         return null;
     }
 
+    @Override
+    public void setThread(int thread) {
+        poolSize=thread;
+    }
+
     private void handleGzip(HttpResponse httpResponse) {
         Header ceheader = httpResponse.getEntity().getContentEncoding();
         if (ceheader != null) {
diff --git a/webmagic-plugin/webmagic-selenium/src/main/java/us/codecraft/webmagic/selenium/downloader/SeleniumDownloader.java b/webmagic-plugin/webmagic-selenium/src/main/java/us/codecraft/webmagic/selenium/downloader/SeleniumDownloader.java
index 54e3c9c0..76ac0508 100644
--- a/webmagic-plugin/webmagic-selenium/src/main/java/us/codecraft/webmagic/selenium/downloader/SeleniumDownloader.java
+++ b/webmagic-plugin/webmagic-selenium/src/main/java/us/codecraft/webmagic/selenium/downloader/SeleniumDownloader.java
@@ -27,12 +27,14 @@ import java.util.Map;
  */
 public class SeleniumDownloader implements Downloader, Destroyable {
 
-    private WebDriverPool webDriverPool;
+    private volatile WebDriverPool webDriverPool;
 
     private Logger logger = Logger.getLogger(getClass());
 
     private int sleepTime = 0;
 
+    private int poolSize = 1;
+
     /**
      * 新建
      *
@@ -40,16 +42,11 @@ public class SeleniumDownloader implements Downloader, Destroyable {
      */
     public SeleniumDownloader(String chromeDriverPath) {
         System.getProperties().setProperty("webdriver.chrome.driver", chromeDriverPath);
-        webDriverPool = new WebDriverPool();
-    }
-
-    public SeleniumDownloader(String chromeDriverPath, int poolSize) {
-        System.getProperties().setProperty("webdriver.chrome.driver", chromeDriverPath);
-        webDriverPool = new WebDriverPool(poolSize);
     }
 
     /**
      * set sleep time to wait until load success
+     *
      * @param sleepTime
      * @return this
      */
@@ -60,6 +57,7 @@ public class SeleniumDownloader implements Downloader, Destroyable {
 
     @Override
     public Page download(Request request, Task task) {
+        checkInit();
         WebDriver webDriver;
         try {
             webDriver = webDriverPool.get();
@@ -93,6 +91,19 @@ public class SeleniumDownloader implements Downloader, Destroyable {
         return page;
     }
 
+    private void checkInit() {
+        if (webDriverPool == null) {
+            synchronized (this){
+                webDriverPool = new WebDriverPool(poolSize);
+            }
+        }
+    }
+
+    @Override
+    public void setThread(int thread) {
+        this.poolSize = thread;
+    }
+
     @Override
     public void destroy() {
         webDriverPool.closeAll();