输入此代码functions.php 文件

add_filter( \'woocommerce_checkout_fields\' , \'rws_display_checkbox_and_new_checkout_field\' ); 
function rws_display_checkbox_and_new_checkout_field( $fields ) {
$fields[\'billing\'][\'have_vat_number\'] = array(
    \'type\'      => \'checkbox\',
    \'label\'     => __(\'Are you have Vat Number?\', \'woocommerce\'),
    \'class\'     => array(\'form-row-wide\'),
    \'clear\'     => true
);   
$fields[\'billing\'][\'vat_number\'] = array(
    \'label\'     => __(\'Vat Number\', \'woocommerce\'),
    \'placeholder\'   => _x(\'Vat Number\', \'placeholder\', \'woocommerce\'),
    \'class\'     => array(\'form-row-wide\'),
    \'clear\'     => true
);
return $fields;
}
add_action( \'woocommerce_after_checkout_form\', \'rws_conditionally_hide_show_new_field\', 9999 );
function rws_conditionally_hide_show_new_field() {
  wc_enqueue_js( "
      jQuery(\'input#have_vat_number\').change(function(){
         if (! this.checked) {
            jQuery(\'#vat_number_field\').fadeOut();
            jQuery(\'#vat_number_field input\').val(\'\');         
         } else {
            jQuery(\'#vat_number_field\').fadeIn();
         } 
      }).change();
  ");   
}
function rws_move_checkout_email_field( $address_fields ) {
    $address_fields[\'have_vat_number\'][\'priority\'] = 1;
    $address_fields[\'vat_number\'][\'priority\'] = 21;
    return $address_fields;
}
add_filter( \'woocommerce_billing_fields\', \'rws_move_checkout_email_field\', 10 , 1 );