<script type="text/javascript">
<!--
document.biao.bbb.value = "云南";//biao是表单名,atc_province是select标签ID,云南是select默认选中项
//-->
</script>
<form name="biao" method="post" action="" enctype="multipart/form-data">
<select name='aaa' id='bbb'>
<option value=''>现有分类</option>
<option value='新疆'>新疆</option>
<option value='云南'>云南</option> //方法二:<option value="云南" <?php if($res=='云南'){echo "selected";}?>>
<option value='西藏'>西藏</option>
<option value='甘肃'>甘肃</option>
<option value='宁夏'>宁夏</option>
<option value='青海'>青海</option>
</select>
</form>