Pardon?
tag.php lists all posts that have a specific tag. If you want to list all posts in a given category, you need to be looking at category.php.
I found the solution myself
My English is not very good. Maybe the solution can understand what I am asking 🙂
posts tagged with the label : <?php single_tag_title(); ?>
<h2> category name 1</h2>
<?php
$current_tag = single_tag_title("", false);
query_posts(array(
'cat'=>'26',
'showposts'=>'3',
'tag_slug__and'=>array($current_tag),
) );
?><?php while (have_posts()) : the_post(); ?>
while....
<?php endwhile; ?>
<h2> category name 2</h2>
<?php
$current_tag = single_tag_title("", false);
query_posts(array(
'cat'=>'27',
'showposts'=>'3',
'tag_slug__and'=>array($current_tag),
) );
?><?php while (have_posts()) : the_post(); ?>
while...
<?php endwhile; ?>
