DefaultButton接收的是一个按钮的ID.
<form id="form1" runat="server" defaultbutton="button1">
<div>
<asp:Panel DefaultButton="button1"></asp:Panel>
<asp:Button ID="button1" runat="server" Text="Button1" />
</div>
</form>
<div>
<asp:Panel DefaultButton="button1"></asp:Panel>
<asp:Button ID="button1" runat="server" Text="Button1" />
</div>
</form>