write = new StreamWriter(file.FullName, false);

------解决方案--------------------

C# code

    /// <param name="FilePath">文件路径</param>
        /// <param name="Content">文件内容</param>
        /// <param name="Append">是否追加</param>
        /// <param name="Encode">文件编码</param>
        public static void WriteFile(string FilePath, string Content, bool Append)
        {
            StreamWriter st = new StreamWriter(FilePath, Append, System.Text.Encoding.GetEncoding("gb2312"));
            st.Write(Content);
            st.Close();
            st.Dispose();
        }