datagrid 控件加 OnItemCommand="SelectIndex" 这个 然后把你 <Columns>
<asp:ButtonColumn   CommandName="modif"       ButtonType="LinkButton" HeaderText="修改信息" Text="修改信息">
<HeaderStyle Font-Size="9" HorizontalAlign="Center" Width="10%"></HeaderStyle>
</asp:ButtonColumn>
<asp:ButtonColumn CommandName="del"     ButtonType="LinkButton" HeaderText="删除信息" Text="删除信息">
<HeaderStyle Font-Size="9" HorizontalAlign="Center" Width="10%"></HeaderStyle>
</asp:ButtonColumn>
</Columns>
CS文件
public void SelectIndex(object sender,DataGridCommandEventArgs e)
{
if(e.CommandName=="modif")
{
 
                             }
else
{
                              }
 

}