<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>无标题 1</title>
<script type="text/javascript" src="Scripts/jquery-1.4.1-vsdoc.js"></script>
</head>
<body>
<form method="post">
<select >
<option value="0"></option>
<option value="1">11</option>
<option value="2">22</option>
<option value="3">33</option>
</select></form>
</body>
<script type="text/javascript" defer="defer">
var doms = document.getElementsByTagName("select");
//doms[0].value="1";
//doms[0].options[2].selected = true;
//jquery方法
$("#s2 option[index=3]").attr("selected", true)
</script>
</html>