document.onkeydown = keydown;
function keydown(e)
{
var currKey=0,e=e||event;
currKey=e.keyCode||e.which||e.charCode;//支持IE、FF
if (currKey == 13){
if(event){
e.returnValue = false;
}else{
e.preventDefault();
}
document.getElementById("<%=btnRegister.ClientID %>").click();
}
}
http://blog.csdn.net/angus_17/article/details/6874990