我想你的问题已经在here

$args = array(\'posts_per_page\' => -1, \'orderby\' => \'date\' );
$myQuery = new WP_Query($args);
$date = \'\';
if ( $myQuery->have_posts() ) : while ( $myQuery->have_posts() ) : $myQuery->the_post();
if ( $date != get_the_date() ) {
    echo $date;
    echo \'<hr />\';
    $date = get_the_date();
}
the_title(); // or whatever you want here.
echo \'<br />\';
endwhile; endif;
wp_reset_postdata();