/// <summary>
        /// 发送SOAP请求，并返回响应xml
        /// </summary>
        /// <param name="url">请求地址</param>
        /// <param name="datastr">SOAP请求信息</param>
        /// <returns>返回响应信息</returns>
        public static string GetSOAPReSource(string url, string datastr)
        {

            //发起请求
            Uri uri = new Uri(url);
            WebRequest webRequest = WebRequest.Create(uri);
            webRequest.ContentType = "text/xml; charset=utf-8";
            webRequest.Method = "POST";
            using (Stream requestStream = webRequest.GetRequestStream())
            {
                byte[] paramBytes = Encoding.UTF8.GetBytes(datastr.ToString());
                requestStream.Write(paramBytes, 0, paramBytes.Length);
            }

            //响应
            WebResponse webResponse = webRequest.GetResponse();
            using (StreamReader myStreamReader = new StreamReader(webResponse.GetResponseStream(), Encoding.UTF8))
            {
                string result = "";
                return result=myStreamReader.ReadToEnd();
            }
        }

示例：调用webservice查询IP地址信息

webservice地址：http://www.wjg121.cn/Service/IPAddress.asmx?op=GetIPCountryAndLocal

      static void Main(string[] args)
        {

             
            //构造soap请求信息
            StringBuilder soap = new StringBuilder();
            soap.Append("<?xml version=\"1.0\" encoding=\"utf-8\"?>");
            soap.Append("<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.Append("<soap:Body>");
            soap.Append("<GetIPCountryAndLocal xmlns=\"http://tempuri.org/\">");
            soap.Append("<RequestIP>183.39.119.90</RequestIP>");
            soap.Append("</GetIPCountryAndLocal>");
            soap.Append("</soap:Body>");
            soap.Append("</soap:Envelope>");

            string url = "http://www.wjg121.cn/Service/IPAddress.asmx";
            Console.WriteLine(WebServiceUtility.GetSOAPReSource(url,soap.ToString()));           
            Console.ReadKey();

        }

//返回结果：

<?xml version="1.0" encoding="utf-8"?><soap:Envelope xmlns:soap="http://schemas.
xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance
" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><soap:Body><GetIPCountryAndLocalR
esponse xmlns="http://tempuri.org/"><GetIPCountryAndLocalResult>广东省电信</GetI
PCountryAndLocalResult></GetIPCountryAndLocalResponse></soap:Body></soap:Envelop
e>

[转]C#通过Http发送Soap请求