public partial class test_updatepaneltest : System.Web.UI.Page
{
    protected void show_it(object sender, EventArgs e)
    {
        ScriptManager my_script = new ScriptManager();
        panel_place.Controls.Add(my_script);

        UpdatePanel mypanel = new UpdatePanel();
        panel_place.Controls.Add(mypanel);

        Button show_btn = new Button();
        show_btn.ID = "button1";
        show_btn.Text = "inside_btn at "+DateTime.Now.Second.ToString();
        mypanel.ContentTemplateContainer.Controls.Add(show_btn);

        Button show_btn2 = new Button();
        show_btn2.ID = "button2";
        show_btn2.Text = "outside_btn at " + DateTime.Now.Second.ToString();
        showplace.Controls.Add(show_btn2);
        
    }
    protected void Page_Load(object sender, EventArgs e)
    {
        Button show_updatepanel = new Button();
        show_updatepanel.Click += new EventHandler(show_it);
        show_updatepanel.Text = "点击这里！";
        showplace.Controls.Add(show_updatepanel);
    }
}

    <form id="form1" runat="server">
    <div>
    <asp:Label ID="showplace" runat="server"></asp:Label><br />
    <asp:Label ID="panel_place" runat="server"></asp:Label>
    </div>
    </form>