我通常用另一种方式来做同样的事情

I normally use another way to do the same

using System.Xml;
using System.Net;
using System.IO;

public static void CallWebService()
{
    var _url = "http://xxxxxxxxx/Service1.asmx";
    var _action = "http://xxxxxxxx/Service1.asmx?op=HelloWorld";

    XmlDocument soapEnvelopeXml = CreateSoapEnvelope();
    HttpWebRequest webRequest = CreateWebRequest(_url, _action);
    InsertSoapEnvelopeIntoWebRequest(soapEnvelopeXml, webRequest);

    // begin async call to web request.
    IAsyncResult asyncResult = webRequest.BeginGetResponse(null, null);

    // suspend this thread until call is complete. You might want to
    // do something usefull here like update your UI.
    asyncResult.AsyncWaitHandle.WaitOne();

    // get the response from the completed web request.
    string soapResult;
    using (WebResponse webResponse = webRequest.EndGetResponse(asyncResult))
    {
        using (StreamReader rd = new StreamReader(webResponse.GetResponseStream()))
        {
            soapResult = rd.ReadToEnd();
        }
        Console.Write(soapResult);        
    }
}

private static HttpWebRequest CreateWebRequest(string url, string action)
{
    HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
    webRequest.Headers.Add("SOAPAction", action);
    webRequest.ContentType = "text/xml;charset="utf-8"";
    webRequest.Accept = "text/xml";
    webRequest.Method = "POST";
    return webRequest;
}

private static XmlDocument CreateSoapEnvelope()
{
    XmlDocument soapEnvelopeDocument = new XmlDocument();
    soapEnvelopeDocument.LoadXml(
    @"<SOAP-ENV:Envelope xmlns:SOAP-ENV=""http://schemas.xmlsoap.org/soap/envelope/"" 
               xmlns:xsi=""http://www.w3.org/1999/XMLSchema-instance"" 
               xmlns:xsd=""http://www.w3.org/1999/XMLSchema"">
        <SOAP-ENV:Body>
            <HelloWorld xmlns=""http://tempuri.org/"" 
                SOAP-ENV:encodingStyle=""http://schemas.xmlsoap.org/soap/encoding/"">
                <int1 xsi:type=""xsd:integer"">12</int1>
                <int2 xsi:type=""xsd:integer"">32</int2>
            </HelloWorld>
        </SOAP-ENV:Body>
    </SOAP-ENV:Envelope>");
    return soapEnvelopeDocument;
}

private static void InsertSoapEnvelopeIntoWebRequest(XmlDocument soapEnvelopeXml, HttpWebRequest webRequest)
{
    using (Stream stream = webRequest.GetRequestStream())
    {
        soapEnvelopeXml.Save(stream);
    }
}