.subNav{overflow:hidden}改成.subNav{display:none}
<script src="http://libs.baidu.com/jquery/1.9.0/jquery.js" type="text/javascript"></script>
<script>
$(function () {
var l=$('.nav>li');
l.hover(function (){$(this).children('ul').show(0)},function (){$(this).children('ul').hide(0)})
});</script>
<script src="http://libs.baidu.com/jquery/1.9.0/jquery.js" type="text/javascript"></script>
<script>
$(function () {
var l=$('.nav>li');
l.hover(function (){$(this).children('ul').show(0)},function (){$(this).children('ul').hide(0)})
});</script>