<!DOCTYPE html>
<html>
<head>
<script>
function valignCell()
{
var x=document.getElementById('myTable').rows[0].cells;
x[0].vAlign="bottom";
}
</script>
</head>
<body>
<table id="myTable" border="1" >
<tr>
<td height="50px">第一个单元格</td>
<td>第二个单元格</td>
</tr>
<tr>
<td height="50px">第三个单元格</td>
<td>第四个单元格</td>
</tr>
</table>
<form>
<input type="button" onclick="valignCell()" value="第一个单元格内容底部对齐">
</form>
</body>
</html>
