谢谢各位。我是用WP_Meta_Query (https://codex.wordpress.org/Class_Reference/WP_Meta_Query)

解决方案：

<?php $query = new WP_Query( array( 
             \'meta_key\' => \'j4cob_yaz_ayarlar_show_on_slider_\',
             \'meta_value\'   => \'show-on-slider\',
             \'posts_per_page\' => 6
             ) ); ?>
   <?php if ( $query->have_posts() ) : while ( $query->have_posts() ) : $query->the_post(); ?>
.
Loop
.
<?php endwhile; 
             wp_reset_postdata();
             else : ?>
            <p><?php _e( \'Sorry, no posts matched your criteria.\' ); ?></p>
          <?php endif; ?>