$re = '/<td ><b>发起时间<\/b><\/td>\s+<td colspan="2" style="text-align: left">([0-9]{4}-[0-9]{2}-[0-9]{2})<\/td>/';
$str = ' <tr>
<td ><b>发起时间</b></td>
<td colspan="2" style="text-align: left">2015-04-08</td>
<td style="width: 25%;"><b>回报机制</b></td>
<td colspan="2" style="text-align: left">使用者付费</td>
</tr>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php