Code
namespace testnt
{
    public class ReadAndWrite
    {
        string encoding;
        public ReadAndWrite(string encoding)
        {
            this.encoding = encoding;
        }
        public ReadAndWrite()
        {
        }
        public string CustomEncode
        {
            get { return encoding; }
            set { encoding = value; }
        }
        public string ReadLocalFile(string fileaddress)
        {
            StreamReader streamreaderobj = new StreamReader(fileaddress, System.Text.Encoding.GetEncoding(CustomEncode));
            string html = streamreaderobj.ReadToEnd();
            streamreaderobj.Close();
            return html;
        }
        public string GetPageToStr(string uri)
        {
            string strHtml;
            StreamReader reader = null;
            Encoding code = Encoding.GetEncoding(this.CustomEncode);
            //构造web请求，发送请求，获取响应   
            WebRequest HttpWebRequest = null;
            WebResponse HttpWebResponse = null;

            HttpWebRequest = WebRequest.Create(uri);
            HttpWebResponse = HttpWebRequest.GetResponse();

            //获得流
            reader = new StreamReader(HttpWebResponse.GetResponseStream(), code);
            strHtml = reader.ReadToEnd();
            return strHtml;
        }
        public bool WriteFile(string Path, string Strings)
        {
            try
            {
                if (!File.Exists(Path))
                {
                    FileStream f = File.Create(Path);
                    f.Close();
                }
                StreamWriter f2 = new StreamWriter(Path, false, Encoding.GetEncoding(this.CustomEncode));
                //此处若改为true,则表示在文本后追加。
                f2.WriteLine(Strings);
                f2.Flush();
                f2.Close();
                f2.Dispose();
                return true;
            }
            catch { return false; }
        }

    }
    
}

调用代码

ReadAndWrite raw = new ReadAndWrite("utf-8");
            string html = raw.ReadLocalFile(Server.MapPath(@"../../template/div-index.html"));
            string remotefile = raw.GetPageToStr(@"http://www.120mmm.com/bbs/tools/showtopics.aspx?count=11&fid=73");
            html = String.Format(html, remotefile);
            raw.WriteFile(Server.MapPath(@"../../h/index.html"), html);