public static string HttpDownloadFile(string url, string path)
    {
        // 设置参数
        HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
        //发送请求并获取相应回应数据
        HttpWebResponse response = request.GetResponse() as HttpWebResponse;
        //直到request.GetResponse()程序才开始向目标网页发送Post请求
        Stream responseStream = response.GetResponseStream();

        //创建本地文件写入流
        Stream stream = new FileStream(path, FileMode.Create);

        byte[] bArr = new byte[1024];
        int size = responseStream.Read(bArr, 0, (int)bArr.Length);
        while (size > 0)
        {
            stream.Write(bArr, 0, size);
            size = responseStream.Read(bArr, 0, (int)bArr.Length);
        }
        stream.Close();
        responseStream.Close();
        return path;
    }