<table border=1 width=200>
<br /><tr>
<br /><td style="word-wrap:break-word; width:100">
<br />dsgdfsddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd
<br /></td>
<br /></tr>
<br /></table>
<br /><tr>
<br /><td style="word-wrap:break-word; width:100">
<br />dsgdfsddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd
<br /></td>
<br /></tr>
<br /></table>
$str = chum_split($str,5,"<br>"); //5个字符换行
echo $str;