The concept of security has changed greatly since the end of the Cold War, Barry Buzan's ”security complex” has represented the change exactly. Through this concept, I try to explore the United Nations Development Program (UNDP) incorporated the Tumen River Area Development Program (TRADP) into one of crucial plans of regional ccooperation and development in 1991, six countries, People's Republic of China, Russian Federation, People's Republic of Korea, Republic of Korea, Mongolia, and Japan reached consensus in the plan, activating the economic cooperation among Northeast Asian countries. With the concept of security complex, we can understand the TRADP pertains not only to interests of participatory countries but also to the contribution from participatory countries to regional security cooperation. The UN's purpose of creating this regional cooperation development program is to promote the locals' life quality, to prevent conflicts effectively, and to foster international peace.