The safety of the Southeast Asian searway is facing more and more serious threat which includes pirate and sea terrorism. Those damage the economic and safety of the members of Association of Southeast Asia, however, each of the members doesn¡¦t have enough power to resist the enemy. When the members of the ASEAN start to solve the problems, the lack of technology and military ability make them dependant on the powerful states extra-Southeast Asia, besides, the limit of the three rules (equality, non-interference in the internal affairs of one another, and unanimity) of ASEAN also obstruct the regionalism. The research which surveys the official and unofficial documents, international organizations, and international law about piracy and sea terrorism finds that the members of ASEAN on the base of the same issue of common interests will cooperate by the way of spill-over. This proves that each members can cooperate from on single issue to form the regionalism.