This paper intends to examine why the financial cooperation is prominently advanced and the trade collaboration is stunted in the ASEAN+3 region. Three factors are presented in order to illuminate the main question: institutional frameworks, decision-making of regional leaders and external challenges. Institutional frameworks can be including regional organizations, institutions or multilateral agreements which have primary purposes on economic cooperation since the WTO system was built. In the ASEAN+3 region, the fact that the ASEAN+3 summit became a regularized annual meeting has consolidated the institutional framework in the region. Although the attempt to build the East Asia Economic Caucus was failed, that played a role in the blueprint of ASEAN+3 summit. The legacy has constantly continued as Chiang Mai Initiative Multilateralization. Generally, regional leaders seek the national economic profit to take economic risk aversion. No matter how proper the intention is, it is hard to achieve the regional economic integration if the influence of states and leaders is not considered. It is notable that the ASEAN+3 summit was successfully settled after China, Japan and South Korea positively participated in the meeting. The Asian financial crisis in the late 1990s is a representative economic external challenge on the region. After the crisis, the regional economy was bound together into a financial cooperation, and the regional liquidity fund, named Chiang Mai Initiative, was created as a starting point of regional economic integration. Whereas financial integration developed rapidly in the ASEAN+3 region, there was no remarkable momentum to stimulate the regional trade cooperation. Those three factors does not affect the regional economic integration respectively. Institutional frameworks were based on the economic integration, and decision-making of regional leaders gave the direction of the integration: finance or trade. The external challenge of the Asian financial crisis provides Asian countries with the most significant stimulation, but the importance of the external challenge cannot lessen the influence of two factors in economic integration.