我面临同样的问题，最终的解决方案，我发现是通过HttpWebRequest的。 样本code：

I was facing the same problem and the final solution I found was through HttpWebRequest. A sample code:

    public string ProcessAttachment(string fileInput)
    {
        HttpWebRequest req = (HttpWebRequest)WebRequest.Create(Settings.Default.GWM_WS_WebReference_GWM);
        req.Headers.Add("SOAPAction", "\"http://www.starstandards.org/webservices/2005/10/transport/operations/ProcessMessage/v1_01/ProcessAttachment\"");
        req.Headers.Add("Accept-Encoding", "gzip,deflate");
        req.ContentType = "multipart/related; type=\"application/xop+xml\"; start=\"<rootpart@soapui.org>\"; start-info=\"text/xml\"; boundary=\"----=_Part_14_1350106.1324254402199\"";
        req.Method = "POST";
        req.UserAgent = "Jakarta Commons-HttpClient/3.1";
        req.Headers.Add("MIME-Version", "1.0");
        System.Net.ServicePointManager.Expect100Continue = false;
        Stream memStream = new System.IO.MemoryStream();
        FileStream fileStream = new FileStream(fileInput, FileMode.Open, FileAccess.Read);
        byte[] buffer = new byte[1024];
        int bytesRead = 0;
        while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
        {
            memStream.Write(buffer, 0, bytesRead);
        }
        fileStream.Close();
        Stream stm = req.GetRequestStream();
        memStream.Position = 0;
        byte[] tempBuffer = new byte[memStream.Length];
        memStream.Read(tempBuffer, 0, tempBuffer.Length);
        memStream.Close();
        stm.Write(tempBuffer, 0, tempBuffer.Length);
        stm.Close();
        HttpWebResponse resp = null;
        resp = (HttpWebResponse)req.GetResponse();
        stm = resp.GetResponseStream();
        StreamReader r = new StreamReader(stm);
        return r.ReadToEnd();            
    }

参数的FileInput是包含​​还含有的文件的原始二进制数据的SOAP请求被附加在末端使用MIME边界

The parameter fileInput is the absolute path of the file that contains the SOAP Request containing also the raw binary data of the file to be attached at the end separated with MIME Boundary