/// <summary>
/// 将本地文件上传到指定的服务器(HttpWebRequest方法)
/// </summary>
/// <param name="address">文件上传到的服务器</param>
/// <param name="fileNamePath">要上传的本地文件（全路径）</param>
/// <param name="saveName">文件上传后的名称</param>
/// <param name="progressBar">上传进度条</param>
/// <returns>成功返回1，失败返回0</returns>
private int Upload_Request(string address, string fileNamePath, string saveName, ProgressBar progressBar)
{
    int returnValue = 0;

    // 要上传的文件
    FileStream fs = new FileStream(fileNamePath, FileMode.Open, FileAccess.Read);
    BinaryReader r = new BinaryReader(fs);

    //时间戳
    string strBoundary = "----------" + DateTime.Now.Ticks.ToString("x");
    byte[] boundaryBytes = Encoding.ASCII.GetBytes("\r\n--" + strBoundary + "\r\n");

    //请求头部信息
    StringBuilder sb = new StringBuilder();
    sb.Append("--");
    sb.Append(strBoundary);
    sb.Append("\r\n");
    sb.Append("Content-Disposition: form-data; name="");
    sb.Append("file");
    sb.Append(""; filename="");
    sb.Append(saveName);
    sb.Append(""");
    sb.Append("\r\n");
    sb.Append("Content-Type: ");
    sb.Append("application/octet-stream");
    sb.Append("\r\n");
    sb.Append("\r\n");
    string strPostHeader = sb.ToString();
    byte[] postHeaderBytes = Encoding.UTF8.GetBytes(strPostHeader);

    // 根据uri创建HttpWebRequest对象
    HttpWebRequest httpReq = (HttpWebRequest)WebRequest.Create(new Uri(address));
    httpReq.Method = "POST";

    //对发送的数据不使用缓存
    httpReq.AllowWriteStreamBuffering = false;

    //设置获得响应的超时时间（默认300秒）
    httpReq.Timeout = 300000;
    httpReq.ContentType = "multipart/form-data; boundary=" + strBoundary;
    long length = fs.Length + postHeaderBytes.Length + boundaryBytes.Length;
    long fileLength = fs.Length;
    httpReq.ContentLength = length;
    try
    {
        progressBar.Maximum = int.MaxValue;
        progressBar.Minimum = 0;
        progressBar.Value = 0;

        //每次上传4k
        int bufferLength = 4096;
        byte[] buffer = new byte[bufferLength];

        //已上传的字节数
        long offset = 0;

        //开始上传时间
        DateTime startTime = DateTime.Now;
        int size = r.Read(buffer, 0, bufferLength);
        Stream postStream = httpReq.GetRequestStream();

        //发送请求头部消息
        postStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);
        while (size > 0)
        {
            postStream.Write(buffer, 0, size);
            offset += size;
            progressBar.Value = (int)(offset * (int.MaxValue / length));
            TimeSpan span = DateTime.Now - startTime;
            double second = span.TotalSeconds;
            lblTime.Text = "已用时：" + second.ToString("F2") + "秒";
            if (second > 0.001)
            {
                lblSpeed.Text = " 平均速度：" + (offset / 1024 / second).ToString("0.00") + "KB/秒";
            }
            else
            {
                lblSpeed.Text = " 正在连接…";
            }
            lblState.Text = "已上传：" + (offset * 100.0 / length).ToString("F2") + "%";
            lblSize.Text = (offset / 1048576.0).ToString("F2") + "M/" + (fileLength / 1048576.0).ToString("F2") + "M";
            Application.DoEvents();
            size = r.Read(buffer, 0, bufferLength);
        }
        //添加尾部的时间戳
        postStream.Write(boundaryBytes, 0, boundaryBytes.Length);
        postStream.Close();

        //获取服务器端的响应
        WebResponse webRespon = httpReq.GetResponse();
        Stream s = webRespon.GetResponseStream();
        StreamReader sr = new StreamReader(s);

        //读取服务器端返回的消息
        String sReturnString = sr.ReadLine();
        s.Close();
        sr.Close();
        if (sReturnString == "Success")
        {
            returnValue = 1;
        }
        else if (sReturnString == "Error")
        {
            returnValue = 0;
        }

    }
    catch
    {
        returnValue = 0;
    }
    finally
    {
        fs.Close();
        r.Close();
    }

    return returnValue;
}

参数说明如下：

address：接收文件的URL地址，如：http://localhost/UploadFile/Save.aspx

fileNamePath：要上传的本地文件，如：D:\test.rar

saveName：文件上传到服务器后的名称，如：200901011234.rar

progressBar：显示文件上传进度的进度条。

接收文件的WebForm添加一个Save.aspx页面，Load方法如下：

protected void Page_Load(object sender, EventArgs e)
{
    if (Request.Files.Count > 0)
    {
        try
        {
            HttpPostedFile file = Request.Files[0];
            string filePath = this.MapPath("UploadDocument") + "\" + file.FileName;
            file.SaveAs(filePath);
            Response.Write("Success\r\n");
        }
        catch
        {
            Response.Write("Error\r\n");
        }
    }
}

同时需要配置WebConfig文件的httpRuntime 如下：

<httpRuntime maxRequestLength="102400" executionTimeout="300"/>

不能的话最大只能上传4M了。要是想上传更大的文件，maxRequestLength，executionTimeout设置大些，同时WinForm下的代码行

//设置获得响应的超时时间（300秒）
httpReq.Timeout = 300000;