在合并的首位置加上colspan或者rowspan属性即可
<html>
<body>
<h4>横跨两列的单元格:</h4>
<table border="1">
<tr>
<th>姓名</th>
<th colspan="2">电话</th>
</tr>
<tr>
<td>Bill Gates</td>
<td>555 77 854</td>
<td>555 77 855</td>
</tr>
</table>
<h4>横跨两行的单元格:</h4>
<table border="1">
<tr>
<th>姓名</th>
<td>Bill Gates</td>
</tr>
<tr>
<th rowspan="2">电话</th>
<td>555 77 854</td>
</tr>
<tr>
<td>555 77 855</td>
</tr>
</table>
</body>
</html>