在您的环境中执行此操作应该可以为标题表格单元格与内容设置正确的宽度。
例子
HTML
<table id="theHeader">
<thead>
<tr>
<th>Test</th>
<th>Test</th>
<th>Test</th>
<th>Test</th>
</tr>
</thead>
</table>
<table id="theContent">
<tbody>
<tr>
<td>Testing</td>
<td>Testing</td>
<td>Testing</td>
<td>Testing</td>
</tr>
</tbody>
</table>
jQuery
var headerColumns = $('#theHeader thead tr:first-child th');
var contentColumns = $('#theContent tbody tr:first-child td');
for(i=0; i<contentColumns.length; i++){
$(headerColumns[i]).css('width',$(contentColumns[i]).width()+'px');
}
jsFiddle
http://jsfiddle.net/xWbhM/