string postString = "spId=123&loginName=xxxxx&password=xxxx&content=测试内容&mobiles=13712345678&subPort=";//这里即为传递的参数
    byte[] postData = Encoding.GBK.GetBytes(postString);//编码，尤其是汉字，事先要看下抓取网页的编码方式  
    string url = "http://www.ems88.cn:8080/sms/Send.do";//接口地址  
    WebClient webClient = new WebClient();  
    webClient.Headers.Add("Content-Type", "application/x-www-form-urlencoded");//采取POST方式必须加的header，如果改为GET方式的话就去掉这句话即可  
    byte[] responseData = webClient.UploadData(url, "POST", postData);//得到返回字符流  
    string srcString = Encoding.UTF8.GetString(responseData);//解码