<script type="text/javascript">
  $(document).ready(function () { 
　　　　$("#op_div").css("padding-top", $("#search_div").height() + 5); //div自动高度
    });
</script>

<div id="search_div" class="tt-attach" style="height: 80px;">
<dl>
        <dd>
            学号：</dd>
        <dt>
           @Html.TextBox("No_Search", "", new
               {
                   style = "width:135px;",
                   title = "请输入学号进行搜索"
               })</dt>
        </dt>
    </dl>
    <dl>
        <dd>
            姓名：</dd>
        <dt>@Html.TextBox("Name_Search", "", new
               {
                   style = "width:135px;",
                   title = "请输入姓名进行搜索"
               })</dt>
    </dl>
　　<input id="btnSearch" class="btns" value="搜索" type="button" />
</div>
<div id="op_div" style="clear:both;"></div> //"clear:both;"清除浮动，避免改变之后内容的布局

.tt-attach dl
{
    width: 220px;
    display: block;
    float: left;
    height: 25px;
    line-height: 30px;
    padding: 0px;
}
.tt-attach dl dd
{
    width: 70px;
    display: block;
    float: left;
    height: 25px;
    line-height: 30px;
    margin: 0px;
    text-align: right;
    padding: 0px;
}
.tt-attach dl dt
{
    width: 150px;
    display: block;
    float: left;
    height: 25px;
    line-height: 30px;
    margin: 0px;
    text-align: right;
    padding: 0px;
}
.tt-attach .btns
{
    display: block;
    float: left;
    padding: 0px;
    margin-left: 10px;
    margin-top: 5px;
}