我最后使用了下面的代码。希望有人觉得这有用。

/* Display only user-uploaded files to each user in Media Library for file upload form*/

function user_restrict_media_library( $wp_query_obj ) {
    global $current_user, $pagenow;
    if( !is_a( $current_user, \'WP_User\') )
        return;
    if( \'admin-ajax.php\' != $pagenow || $_REQUEST[\'action\'] != \'query-attachments\' )
        return;
    if( !current_user_can(\'manage_media_library\') )
        $wp_query_obj->set(\'author\', $current_user->ID );
    return;
}
add_action(\'pre_get_posts\',\'user_restrict_media_library\');