实现代码来源于网络，我只是作了一些修改！

using System;using System.Web;using System.Xml;using System.Collections;using System.Net;using System.Text;using System.IO;using System.Xml.Serialization;/// <summary>///  利用WebRequest/WebResponse进行WebService调用的类/// </summary>public class WebServiceHelper{    //<webServices>    //  <protocols>    //    <add name="HttpGet"/>    //    <add name="HttpPost"/>    //  </protocols>    //</webServices>    private static Hashtable _xmlNamespaces = new Hashtable();//缓存xmlNamespace，避免重复调用GetNamespace    /// <summary>    /// 需要WebService支持Post调用    /// </summary>    public static XmlDocument QueryPostWebService(String URL, String MethodName, Hashtable Pars)    {        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(URL + "/" + MethodName);        request.Method = "POST";        request.ContentType = "application/x-www-form-urlencoded";        SetWebRequest(request);        byte[] data = http://www.mamicode.com/EncodePars(Pars);"/" + MethodName + "?" + ParsToString(Pars));        request.Method = "GET";        request.ContentType = "application/x-www-form-urlencoded";        SetWebRequest(request);        return ReadXmlResponse(request.GetResponse());    }    /// <summary>    /// 通用WebService调用(Soap),参数Pars为String类型的参数名、参数值    /// </summary>    public static XmlDocument QuerySoapWebService(String URL, String MethodName, Hashtable Pars)    {        if (_xmlNamespaces.ContainsKey(URL))        {            return QuerySoapWebService(URL, MethodName, Pars, _xmlNamespaces[URL].ToString());        }        else        {            return QuerySoapWebService(URL, MethodName, Pars, GetNamespace(URL));        }    }    /// <summary>    /// 通用WebService调用(Soap)    /// </summary>    /// <param name="URL"></param>    /// <param name="MethodName"></param>    /// <param name="Pars"></param>    /// <param name="XmlNs"></param>    /// <returns></returns>    private static XmlDocument QuerySoapWebService(String URL, String MethodName, Hashtable Pars, string XmlNs)    {        _xmlNamespaces[URL] = XmlNs;//加入缓存，提高效率        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(URL);        request.Method = "POST";        request.ContentType = "text/xml; charset=utf-8";        request.Headers.Add("SOAPAction", "\"" + XmlNs + (XmlNs.EndsWith("/") ? "" : "/") + MethodName + "\"");        SetWebRequest(request);        byte[] data = http://www.mamicode.com/EncodeParsToSoap(Pars, XmlNs, MethodName);"soap", "http://schemas.xmlsoap.org/soap/envelope/");        String RetXml = doc.SelectSingleNode("//soap:Body/*/*", mgr).InnerXml;        doc2.LoadXml("<root>" + RetXml + "</root>");        AddDelaration(doc2);        return doc2;    }    /// <summary>    /// 通过WebService的WSDL获取XML名称空间    /// </summary>    /// <param name="URL"></param>    /// <returns></returns>    private static string GetNamespace(String URL)    {        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL + "?WSDL");        SetWebRequest(request);        WebResponse response = request.GetResponse();        StreamReader sr = new StreamReader(response.GetResponseStream(), Encoding.UTF8);        XmlDocument doc = new XmlDocument();        doc.LoadXml(sr.ReadToEnd());        sr.Close();        return doc.SelectSingleNode("//@targetNamespace").Value;    }    /// <summary>    /// 动态生成SOP请求报文内容    /// </summary>    /// <param name="Pars"></param>    /// <param name="XmlNs"></param>    /// <param name="MethodName"></param>    /// <returns></returns>    private static byte[] EncodeParsToSoap(Hashtable Pars, String XmlNs, String MethodName)    {        XmlDocument doc = new XmlDocument();        doc.LoadXml("<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\"></soap:Envelope>");        AddDelaration(doc);        XmlElement soapBody = doc.CreateElement("soap", "Body", "http://schemas.xmlsoap.org/soap/envelope/");        XmlElement soapMethod = doc.CreateElement(MethodName);        soapMethod.SetAttribute("xmlns", XmlNs);        foreach (string k in Pars.Keys)        {            XmlElement soapPar = doc.CreateElement(k);            soapPar.InnerXml = ObjectToSoapXml(Pars[k]);            soapMethod.AppendChild(soapPar);        }        soapBody.AppendChild(soapMethod);        doc.DocumentElement.AppendChild(soapBody);        return Encoding.UTF8.GetBytes(doc.OuterXml);    }    /// <summary>    /// 将对象转换成XML节点格式    /// </summary>    /// <param name="o"></param>    /// <returns></returns>    private static string ObjectToSoapXml(object o)    {        XmlSerializer mySerializer = new XmlSerializer(o.GetType());        MemoryStream ms = new MemoryStream();        mySerializer.Serialize(ms, o);        XmlDocument doc = new XmlDocument();        doc.LoadXml(Encoding.UTF8.GetString(ms.ToArray()));        if (doc.DocumentElement != null)        {            return doc.DocumentElement.InnerXml;        }        else        {            return o.ToString();        }    }    /// <summary>    /// 设置WEB请求    /// </summary>    /// <param name="request"></param>    private static void SetWebRequest(HttpWebRequest request)    {        request.Credentials = CredentialCache.DefaultCredentials;        request.Timeout = 10000;    }    /// <summary>    /// 设置请求数据    /// </summary>    /// <param name="request"></param>    /// <param name="data"></param>    private static void WriteRequestData(HttpWebRequest request, byte[] data)    {        request.ContentLength = data.Length;        Stream writer = request.GetRequestStream();        writer.Write(data, 0, data.Length);        writer.Close();    }    /// <summary>    /// 获取字符串的UTF8码字符串    /// </summary>    /// <param name="Pars"></param>    /// <returns></returns>    private static byte[] EncodePars(Hashtable Pars)    {        return Encoding.UTF8.GetBytes(ParsToString(Pars));    }    /// <summary>    /// 将Hashtable转换成WEB请求键值对字符串    /// </summary>    /// <param name="Pars"></param>    /// <returns></returns>    private static String ParsToString(Hashtable Pars)    {        StringBuilder sb = new StringBuilder();        foreach (string k in Pars.Keys)        {            if (sb.Length > 0)            {                sb.Append("&");            }            sb.Append(HttpUtility.UrlEncode(k) + "=" + HttpUtility.UrlEncode(Pars[k].ToString()));        }        return sb.ToString();    }    /// <summary>    /// 获取Webservice响应报文XML    /// </summary>    /// <param name="response"></param>    /// <returns></returns>    private static XmlDocument ReadXmlResponse(WebResponse response)    {        StreamReader sr = new StreamReader(response.GetResponseStream(), Encoding.UTF8);        String retXml = sr.ReadToEnd();        sr.Close();        XmlDocument doc = new XmlDocument();        doc.LoadXml(retXml);        return doc;    }    /// <summary>    /// 设置XML文档版本声明    /// </summary>    /// <param name="doc"></param>    private static void AddDelaration(XmlDocument doc)    {        XmlDeclaration decl = doc.CreateXmlDeclaration("1.0", "utf-8", null);        doc.InsertBefore(decl, doc.DocumentElement);    }}

以上是在不引用WEB服务的条件下动态调用WEB服务方法，如果该服务地址不确定或后期有可能会变动，则采用上述这些方法会比较好，当然如果服务地址不会出现变更的情况下，可以在VS中直接引用WEB服务，然后就可调用自动生成的SOAPClient类来调用相应的WEB服务方法，这样就简单很多，如下：

avar client = new SmsService.wmgwSoapClient(); //wmgwSoapClient就是引用WEB服务后自动生成的类                string result = client.MongateSendSubmit(tuserId.Text, tpassword.Text, tpszMobis.Text, tpszMsg.Text, int.Parse(tiMobiCount.Text),                                tpszSubPort.Text, tMsgId.Text);

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C# 通过Get、Post、Soap调用WebService的方法