The reform of ISDS appellate mechanism is the focus in the field of international investment dispute settlement. From the theoretical starting point to the system design, and then to the position of various countries, there are obvious divergences of opinion. As for the theoretical starting point, discussions mainly focus on the capability of the appellate body in dealing with the inconsistency and the incorrectness of current ISDS mechanism, and on the issues of finality and efficiency. As for the design of ISDS appellate system, the divergences mainly lie in the scope and standard of review, the effectiveness of appeal, the selection and appointment of adjudicators, and the implementation mechanism. Since the ISDS reform is led by governments, states play an important role in this process and show different path preferences. The divergence of the reform ISDS appellate mechanism fundamentally reflects that the rule of law in international investment is evolving into a new balance around the