添加category_name or cat 在您的arguments (args)数组。
<div id="mini_stream">
    <ul>
<? $args = array(
    \'post_type\' => \'post\',
    \'posts_per_page\' => 4,
    \'category_name\'=>\'html\',
);
$loop = new wp_Query($args);
while($loop->have_posts()) : $loop->the_post();
    echo \'<a href="\'.get_permalink().\'">\';
    echo get_the_post_thumbnail($post->ID, \'category-thumb\');
    the_title( \'<h6>\', \'</h6>\' );
    echo \'</a>\';
endwhile;
wp_reset_query(); ?>
    </ul>
</div>