$str=<<<htm
<td>1234567890</td>
<td>1234567890123</td>
<td>0987654321</td>
<td>3210987654321</td>
<td>1324354657</td>
<td>1324354657689</td>
htm;

preg_match('/(<td>[\d]{10}<\/td>)/',$str,$match);
print_R ($match[1]);

------解决方案--------------------
PHP code
<?php
$str=<<<htm
<td>1234567890</td>
<td>1234567890123</td>
<td>0987654321</td>
<td>3210987654321</td>
<td>1324354657</td>
<td>1324354657689</td>
htm;

preg_match_all('/(<td>[\d]{10}\b<\/td>)/',$str,$match);
print_R ($match[1]);

------解决方案--------------------
PHP code
preg_match_all('/<td>(\d{10}\b)<\/td>/',$str,$matchs);
print_r ($matchs);

------解决方案--------------------
把函数改成 preg_match_all 就行了

preg_match_all('/(<td>[\d]{10}<\/td>)/',$str,$match);