<script type="text/javascript">
function doZoom(size)
{document.getElementById('zoom').style.fontSize=size+'px';}
</script>
<span id="zoom">需要指定大小的文字</span>
<a href="javascript:doZoom(16)">大</a> <a href="javascript:doZoom(14)">中</a> <a href="javascript:doZoom(12)">小</a>