Imperfect investment cooperation mechanism is the main legal reason leading to unbalanced investment situations among China, Japan and South Korea. Having negotiations for improvement among such three countries under the framework of China-Japan-South Korea free trade area will not balance (one is China, the other is Japan and South Korea) interests of the three parties or reach a compromise. However, China-Japan-South Korea area can be embedded in geographical region of Northeast Asia against the background of multilateral investment rules and the Belt and Road Initiatives, which seems to be more likely to balance interests and reaching compromises. What’s more, following certain principles, finding appropriate platform (Asian Infrastructure Investment Bank) for funding and financing as well as enlarging government involvement in the Greater Tumen Initiative (GTI) can be seen as a strategy for breaking the dilemma in mechanism improvement in investment cooperation among China, Japan and South Korea.