Differential measures towards countries out of the region can threaten the multilateral system and this could be an implicit factor in regionalism. But from the other prospect, economical cooperation among regions would increase the economic welfare and strengthen WTO free trade system. Open Regionalism impelled by WTO can be regarded as a typical example of this. By boosting the liberalization of regional trade investment, APEC promotes the unification of global economy also facilitate the establishment of international economical order. Meanwhile, APEC helps WTO, which aims at free and fair trade, quite a lot. At the same time, by balancing competition and corporation between regions, APEC also remedies several problems of multilateral system which are mainly problems with competition. Korea should be involved positively in implementing and improving the plans which are executed both individually or together in order to promote the in-discrimination in the early stage and extend the idea of open regionalism and win the trust of the foreign countries and improve the commercial environment.