There is difference of “National Status” between World Trade Organization (WTO) system and investment agreement field, there are different explanation methods when an arbitral court of International Center for Settlement of Investment Dispute (ICSID) uses WTO rules, and in addition, the arbitral court has big free ruling right, which result in the inconsistency of the decision of international investment arbitration and which make the efficacy of international arbitral agencies such as ICSID and so on decrease. The difference on “National Status” in investment arbitration mainly focuses on how to use the concept of “competition” to determine whether a foreign investor and a local investor are in “similar condition”, as a result, the authority of ICSID has been challenged, the investment arbitration urgently needs to be reformed and a universal multilateral international investment rule under WTO system should be established so that the arbitral court can makes accurate and uniform explanation when the related WTO rules are used.