您需要使用pre\\u get\\u posts挂钩。其中，您可以在其他类别页面上包含默认类别帖子。

function wpse_pre_get_posts( $q )
{
    // its the main query, and its the category page archive
    if( $q->is_main_query() && $q->is_category() ) :

        // get the default selected category id, fallback to 1 (default one id)
        $default_cat = (int) get_option(\'default_category\', 1);

        // if the category page is not the default category page
        if( $default_cat != $q->get_queried_object_id() ):

            // get the already used tax_query arguments
            $tax_query = $q->get(\'tax_query\');

            // add the default one
            $tax_query[] = array(
                \'taxonomy\' => \'category\', 
                \'field\'    => \'term_id\', 
                \'terms\'    => $default_cat 
            );

            // relation should be or, which means either the current category or the default
            $tax_query[\'relation\'] = \'OR\';

            // set the values to query
            $q->set(\'tax_query\', $tax_query );

        endif;

    endif;
}
add_action( \'pre_get_posts\', \'wpse_pre_get_posts\' );

function wpse_posts_request( $request, $q )
{
    global $wpdb;

    // its the main query, and its the category page archive
    if( $q->is_main_query() && $q->is_category() ) :

        // get the default selected category id, fallback to 1 (default one id)
        $default_cat = (int) get_option(\'default_category\', 1);

        // category now
        $cat_now = $q->get(\'cat\');

        // if the category page is not the default category page
        if( $default_cat != $cat_now ):

            $request = str_replace("$wpdb->term_relationships.term_taxonomy_id IN ($cat_now)", "$wpdb->term_relationships.term_taxonomy_id IN ($cat_now, $default_cat)", $request);

        endif;

    endif;

    return $request;
}
add_filter( \'posts_request\', \'wpse_posts_request\', 10, 2 );