C#创建TXT文本文件产生乱码的问题

FileStream f = new FileStream(Server.MapPath("ConfigSiteInfo.txt"),FileMode.OpenOrCreate);
StreamWriter SW = new StreamWriter(f,Encoding.GetEncoding("gb2312"));
SW.WriteLine(“文本”);
SW.Flush();
SW.Close();只以GB2312编码，怎么解决？