protected void Page_Load(object sender, EventArgs e)
    {
        using(StreamWriter sw = new StreamWriter(Request.PhysicalApplicationPath+"index.html",false,System.Text.Encoding.GetEncoding("gb2312")))
        {
            sw.Write(getHtml("http://www.goudiannao.com/Default.aspx", "gb2312"));
        }
    }
    private string getHtml(string url, string charSet)//url是要访问的网站地址，charSet是目标网页的编码，如果传入的是null或者""，那就自动分析网页的编码
    {

        WebClient myWebClient = new WebClient();    //创建WebClient实例myWebClient

        //            需要注意的：

        //有的网页可能下不下来，有种种原因比如需要cookie,编码问题等等

        //这是就要具体问题具体分析比如在头部加入cookie

        // webclient.Headers.Add("Cookie", cookie);

        //这样可能需要一些重载方法。根据需要写就可以了

        //获取或设置用于对向 Internet 资源的请求进行身份验证的网络凭据。

        myWebClient.Credentials = CredentialCache.DefaultCredentials;

        //如果服务器要验证用户名,密码

        //NetworkCredential mycred = new NetworkCredential(struser, strpassword);

        //myWebClient.Credentials = mycred;

        //从资源下载数据并返回字节数组。（加@是因为网址中间有"/"符号）

        byte[] myDataBuffer = myWebClient.DownloadData(url);

        string strWebData = Encoding.Default.GetString(myDataBuffer);

        //获取网页字符编码描述信息

        Match charSetMatch = Regex.Match(strWebData, "<meta([^<]*)charset=([^<]*)\"", RegexOptions.IgnoreCase | RegexOptions.Multiline);

        string webCharSet = charSetMatch.Groups[2].Value;

        if (charSet == null || charSet == "")

            charSet = webCharSet;

        if (charSet != null && charSet != "" && Encoding.GetEncoding(charSet) != Encoding.Default)

            strWebData = Encoding.GetEncoding(charSet).GetString(myDataBuffer);

        return strWebData;

    }