在阅读了PHP和wordpress codex之后，我通过创建一个walker类实现了我想要的。这是代码

class Hambos_Walker_Nav_Menu extends Walker_Nav_Menu {

    function start_lvl( &$output, $depth = 0, $args = array() ) {
        $indent = str_repeat("\\t", $depth);

        if ($depth == 0):
            $output .= "\\n$indent <div>\\n";
        else:
            $output .= "\\n$indent <ul>\\n";
        endif;        

    }

    function end_lvl( &$output, $depth = 0, $args = array() ) {
        $indent = str_repeat("\\t", $depth);

        if ($depth == 0):
            $output .= "$indent</div>\\n";
        else:
            $output .= "$indent</ul>\\n";
        endif;  

    }

    function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
        $indent = ( $depth ) ? str_repeat( "\\t", $depth ) : \'\';

        $class_names = \'\';

        $classes = empty( $item->classes ) ? array() : (array) $item->classes;
        $classes[] = \'menu-item-\' . $item->ID;

        $class_names = join( \' \', apply_filters( \'nav_menu_css_class\', array_filter( $classes ), $item, $args ) );
        $class_names = $class_names ? \' class="\' . esc_attr( $class_names ) . \'"\' : \'\';

        $id = apply_filters( \'nav_menu_item_id\', \'menu-item-\'. $item->ID, $item, $args );
        $id = $id ? \' id="\' . esc_attr( $id ) . \'"\' : \'\';

        if ($depth == 0):
            $output .= $indent . \'<li\' . $id . $class_names .\'><h4>\';
        else:
            $output .= $indent . \'<span\' . $id . $class_names .\'>\';
        endif;

        $atts = array();
        $atts[\'title\']  = ! empty( $item->attr_title ) ? $item->attr_title : \'\';
        $atts[\'target\'] = ! empty( $item->target )     ? $item->target     : \'\';
        $atts[\'rel\']    = ! empty( $item->xfn )        ? $item->xfn        : \'\';
        $atts[\'href\']   = ! empty( $item->url )        ? $item->url        : \'\';

        $atts = apply_filters( \'nav_menu_link_attributes\', $atts, $item, $args );

        $attributes = \'\';
        foreach ( $atts as $attr => $value ) {
            if ( ! empty( $value ) ) {
                $value = ( \'href\' === $attr ) ? esc_url( $value ) : esc_attr( $value );
                $attributes .= \' \' . $attr . \'="\' . $value . \'"\';
            }
        }

        $item_output = $args->before;
        $item_output .= \'<a\'. $attributes .\'>\';
        $item_output .= $args->link_before . apply_filters( \'the_title\', $item->title, $item->ID ) . $args->link_after;
        $item_output .= \'</a>\';
        $item_output .= $args->after;

        $output .= apply_filters( \'walker_nav_menu_start_el\', $item_output, $item, $depth, $args );

    }

    function end_el( &$output, $item, $depth = 0, $args = array() ) {
        if ($depth == 0):
            $output .= "<h4></li>\\n";
        else:
            $output .= "</span>\\n";
        endif;
    }

}