As Cambodia joined ASEAN in 1999, long conflict between Communist and Non-Communist in Southeast Asia since Cold-War ceased and the region merged into the regional organization, ASEAN. Though ASEANization of Southeast Asia greatly reduced the conflict of security in the region, it faces an even bigger challenge and crisis in the external. 'Terror', ‘political split', ‘Globalization' have emerged as main issues in Southeast Asian security. ASEAN has been seeking the forward security strategy with an active responding to the rapid changes of security circumstance. First, strengthening binding within the organization. The second trait of ASEAN security strategy is 'Balancing Powers among Super Power Countries'. While admitting the cooperation with external super powers(USA, Japan, China and India)inevitable, ASEAN won't allow any of these countries to have a sole leadership in the area.In the Future, Korea and ASEAN may share the role for performing as buffer zone, in between China and Japan competition by playing a critical role on Asia security. Korea and ASEAN will be able to play stable buffer roles in the long term until the efficient cooperation is established between two parties.