我找不到钩子，所以我选择了JS选项。

add_action( "admin_head-post-new.php", \'meta_box_instruction\' ); //new post
add_action( "admin_head-post.php", \'meta_box_instruction\' );    //edit post
function meta_box_instruction($d) { 
global $post;

    if($post->post_type == \'{YOUR POST TYPE}\' || $_GET[\'post_type\'] == \'{YOUR POST TYPE}\'):
    ?>

    <script type=\'text/javascript\'>
        jQuery(document).ready(function(){
            jQuery(\'<p>Some instruction</p>\').insertBefore(\'#taxonomy-{YOUR TAXONOMY NAME}\').parent();
        });
    </script>

    <?php
    endif;
}