html:
<table class="b">
<thead>
<tr>
<th>姓名</th>
<th>年龄</th>
<th>性别</th>
</tr>
<tr>
<td>我</td>
<td>11</td>
<td>男</td>
</tr>
<tr>
<td>你</td>
<td>12</td>
<td>女</td>
</tr>
<tr>
<td>他</td>
<td>13</td>
<td>男</td>
</tr>
</thead>
</table>
js:
<script>
$('tr:odd').css({ background: 'red' })
</script>
效果: