<asp:TemplateField HeaderText="备注?" ItemStyle-HorizontalAlign="Left">
                              <ItemTemplate> 
                                      <%#Eval("Remark").ToString().Length > 20 ? Eval("Remark").ToString().Substring(0, 20) + "..." : Eval("Remark")%>  
                              </ItemTemplate> 
                          </asp:TemplateField>

------解决方案--------------------

C# code
    public string DealAddress(string address)
    { 
        string str = "";
        if (address == "")
        {
            str = "";
            return str;
        }
        if (address != "" && address.Length > 20)
        {
            str = address.Substring(0, 20) + "...";
        }
        else
        {
            str = address;
        }
        return str;
    }

------解决方案--------------------
显示固定的几个字，后面用省略号... ...