The United States regards the ruling of the Appellate Body on“issuing not necessary for the settlement of a dispute”as advisory opinions and continues to criticize it, which has aroused widespread concern in the international community. The unnecessary ruling called by the United States is neither an advisory opinion, nor in most cases unnecessary. The Appellate Body must address each legal issue raised during the appeal and clarify existing WTO rules so as to provide security and predictability for the multilateral trading system. Whether a ruling is necessary for the resolution of dispute falls within the discretion of the Appellate body. The most so-called advisory opinions issued by the Appellate Body have important functions of effectively resolving and preventing disputes.