一般可在Page_Load事件里定义排序字段和排序升降顺序，例如：

protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                //排序字段，降序、升序
                ViewState["SortExp"] = "MONTH";
                ViewState["SortDir"] = "ASC";

            }
        }

然后定义GridView_Sorting事件，其实是对DataTable排序，因为GridView的数据源是DataTable

 //排序事件
        protected void GridView_Sorting(object sender, GridViewSortEventArgs e)
        {
            DataSet ds = new DataSet();
            //下面省略一千行
           

                   if (ViewState["SortDir"].ToString().Equals("ASC"))
                    {
                        ViewState["SortDir"] = "DESC";
                        dt.DefaultView.Sort = e.SortExpression + " DESC";
                        this.gv.Columns[0].HeaderText =  this.gv.Columns[0].HeaderText 
                                            + "▼";
                    }
                    else
                    {
                        ViewState["SortDir"] = "ASC";
                        dt.DefaultView.Sort = e.SortExpression + " ASC";
                        this.gv.Columns[0].HeaderText =  this.gv.Columns[0].HeaderText + "▲";
                    }

            this.gv.DataSource = dt.DefaultView;
            this.gv.DataBind();

       }