=====================================前台代码

<input type="button" onclick ="aa();" value="点击" />
<script type="text/javascript">
function aa() {
var bu = document.getElementById("Button1");
bu.click();
}
</script>
<asp:Button ID="Button1" runat ="server" OnClick ="button1_click" />

=====================================后台代码

protected void button1_click(object sender, EventArgs e)
{
ClientScript.RegisterStartupScript(this.GetType(), "", "<script>alert('对不起，没有此人！！！')</script>");
}

访问修饰符是protected 或public