protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
         if (e.Row.RowState == (DataControlRowState.Edit | DataControlRowState.Alternate)
             || e.Row.RowState == DataControlRowState.Edit)
        {
            TextBox curText;
            for (int i = 0; i < e.Row.Cells.Count; i++)
            {
                if (e.Row.Cells[i].Controls.Count != 0)
                {
                    curText = e.Row.Cells[i].Controls[0] as TextBox;
                    if (curText != null)
                    {
                        curText.Width = Unit.Pixel(70);
                    }
                }
            }
        }   

    }

------解决方案--------------------
前台就是这样子了
  <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
          <Columns>
           <asp:TemplateField HeaderStyle-Width="200px" HeaderText="第一列">
               <ItemTemplate>
                   这是第一列
               </ItemTemplate>
           </asp:TemplateField>
            <asp:TemplateField HeaderStyle-Width="50px" HeaderText="第二列">
               <ItemTemplate>
                   这是第二列
               </ItemTemplate>
           </asp:TemplateField>
          </Columns>
  </asp:GridView>

后台设置宽度，就是4楼了，支持4楼。