@kamaraju2407 The problem occurs because the table is nested into another table. Your HTML looks like this:
<table>
<tr>
<td>
<table>
<thead>
<tr><th>qqqqqq</th><th>qqqqqq</th><th>qqqqqq</th></tr>
</thead>
<tbody>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
</tbody>
</table>
</td>
</tr>
</table>
In MS Word Repeat as header row at the top of each page
option does not work for nested tables. If you modify your HTML like this:
<table>
<thead>
<tr><th>qqqqqq</th><th>qqqqqq</th><th>qqqqqq</th>
</tr>
</thead>
<tbody>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
<tr><td>qqqqqq</td><td>qqqqqq</td><td>qqqqqq</td></tr>
</tbody>
</table>
Header row will be repeated properly.