此处内容传输都是用UTF-8编码

1.不带参数发送Post请求

        /// <summary>
        /// 指定Post地址使用Get 方式获取全部字符串
        /// </summary>
        /// <param name="url">请求后台地址</param>
        /// <returns></returns>
        public static string Post(string url)
        {
            string result = "";
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
            req.Method = "POST";
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
            Stream stream = resp.GetResponseStream();
            //获取内容
            using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
            {
                result = reader.ReadToEnd();
            }
            return result;
        }

2.带参数Post请求,指定键值对

        /// <summary>
        /// 指定Post地址使用Get 方式获取全部字符串
        /// </summary>
        /// <param name="url">请求后台地址</param>
        /// <returns></returns>
        public static string Post(string url,Dictionary<string,string> dic)
        {
            string result = "";
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
            req.Method = "POST";
            req.ContentType = "application/x-www-form-urlencoded";
            #region 添加Post 参数
            StringBuilder builder = new StringBuilder();
            int i = 0;
            foreach (var item in dic)
            {
                if (i > 0)
                    builder.Append("&");
                builder.AppendFormat("{0}={1}", item.Key, item.Value);
                i++;
            }
            byte[] data = Encoding.UTF8.GetBytes(builder.ToString());
            req.ContentLength = data.Length;
            using (Stream reqStream = req.GetRequestStream())
            {
                reqStream.Write(data, 0, data.Length);
                reqStream.Close();
            }
            #endregion
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
            Stream stream = resp.GetResponseStream();
            //获取响应内容
            using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
            {
                result = reader.ReadToEnd();
            }
            return result;
        }

3.带参数的Post请求，指定发送字符串内容

/// <summary>
/// 指定Post地址使用Get 方式获取全部字符串
/// </summary>
/// <param name="url">请求后台地址</param>
/// <param name="content">Post提交数据内容(utf-8编码的)</param>
/// <returns></returns>
public static string Post(string url, string content)
{
    string result = "";
    HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
    req.Method = "POST";
    req.ContentType = "application/x-www-form-urlencoded";

    #region 添加Post 参数
    byte[] data = Encoding.UTF8.GetBytes(content);
    req.ContentLength = data.Length;
    using (Stream reqStream = req.GetRequestStream())
    {
        reqStream.Write(data, 0, data.Length);
        reqStream.Close();
    }
    #endregion

    HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
    Stream stream = resp.GetResponseStream();
    //获取响应内容
    using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
    {
        result = reader.ReadToEnd();
    }
    return result;
}

转载方法：

 HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create("http://fanyi.baidu.com/transcontent");
            Encoding encoding = Encoding.UTF8;
            string param = "ie=utf-8&source=txt&query=hello&t=1327829764203&token=8a7dcbacb3ed72cad9f3fb079809a127&from=auto&to=auto";
            //encoding.GetBytes(postData);
            byte[] bs = Encoding.ASCII.GetBytes(param);
            string responseData = String.Empty;            
            req.Method = "POST";
            req.ContentType = "application/x-www-form-urlencoded";
            req.ContentLength = bs.Length;
            using (Stream reqStream = req.GetRequestStream())
            {
                reqStream.Write(bs, 0, bs.Length);
                reqStream.Close();
            }
            using (HttpWebResponse response = (HttpWebResponse)req.GetResponse())
            {
                using (StreamReader reader = new StreamReader(response.GetResponseStream(),encoding))
                {
                    responseData = reader.ReadToEnd().ToString();
                }
                context.Response.Write(responseData);
            }