<script language="javascript">

  function EnterTextBox(button)

  {

  if(event.keyCode == 13 && document.all["TextBox1"].value != "")

  {

  event.keyCode = 9;

  event.returnValue = false;

  document.all[button].click();

  }

  }  

</script>

<asp:TextBox ID="txt1" runat="server"></asp:TextBox>
<asp:Button ID="'Button1'" runat="server" Text="Button1" />
在page_load 事件中加入
TextBox1.Attribute.add("onkeypress","EnterTextBox('Button1')");