如果可以使用javascript，可以在functions.php 文件：

add_action(\'admin_footer\', \'my_admin_footer\');
function my_admin_footer()
{
    $uri = isset($_SERVER[\'REQUEST_URI\']) ? $_SERVER[\'REQUEST_URI\'] : NULL ;

    $message = NULL;

    if ($uri AND strpos($uri,\'edit.php\'))
    {
        if (strpos($uri,\'post_type=page\'))
        {
            $message = \'My custom message for page list\';
        }
        else
        {
            $message = \'My custom message for post list\';
        }
    }

    elseif ($uri AND strpos($uri,\'post-new.php\'))
    {
        if (strpos($uri,\'post_type=page\'))
        {
            $message = \'My custom message for add/edit page\';
        }
        else
        {
            $message = \'My custom message for add/edit post\';
        }
    }

    elseif ($uri AND strpos($uri,\'post.php\'))
    {
        $message = \'My custom message for add/edit post or page\';
    }

    if ($message)
    {
        ?><script>
            jQuery(function($)
            {
                $(\'<div style="margin-bottom:15px; color:#999;"></div>\').text(\'<?php echo $message; ?>\').insertAfter(\'#wpbody-content .wrap h2:eq(0)\');
            });
        </script><?php
    }
}