string str = "Flyso.CN";
        if (!Directory.Exists(Server.MapPath("~\\FLYSO_Log")))
        {
            Directory.CreateDirectory(Server.MapPath("~\\FLYSO_Log"));
        }

        using (StreamWriter sw = new StreamWriter(Server.MapPath(@"~\FLYSO_Log\" + System.DateTime.Now.Year + "-" + System.DateTime.Now.Month + "-" + System.DateTime.Now.Day + ".txt"), true))
        {
            sw.WriteLine(System.DateTime.Now.ToString().Trim() + ":" + str);
            sw.Flush();
            sw.Close();
            sw.Dispose();
        }