你需要一些东西。A.shortcode handler, 和acustom query:

function wpse_186346_excerpt_length() {
    return 50;
}

function wpse_186346_excerpt( $atts ) { 
    $atts = wp_parse_args( $atts,
        array(
            \'posts_per_page\' => 2,
            // Any other default arguments
        )
    );

    // We don\'t need paging, always save a query
    $atts[\'no_found_rows\'] = true;

    // Create query based off arguments from shortcode  
    $query = new WP_Query( $atts );

    // Start the buffer to "catch" our output below, so that we can return it as a string
    ob_start();

    // Set our custom excerpt length
    add_filter( \'excerpt_length\', \'wpse_186346_excerpt_length\' );

    // Loop over the posts and output whatever markup you need
    while ( $query->have_posts() ) {
        $query->the_post();
        the_title( \'<h4 class="excerpt-title"><a href="\' . get_permalink() . \'">\', \'</a></h4>\' );
        the_excerpt();  
    }

    // Remove our custom excerpt length
    remove_filter( \'excerpt_length\', \'wpse_186346_excerpt_length\' );

    // Restore the current global post
    wp_reset_postdata();

    return ob_get_clean();  
}

add_shortcode( \'excerpt\', \'wpse_186346_excerpt\' );

[excerpt tag="test_tag"]