This article explores the Northeast Asian regional security cooperation from the view of constructivist theory, and hence discusses the pathway of advancing the cooperation and building regional security mechanism using its ”International Security Cooperation” theory. Combining the theories of Copenhagen School and Cooperative Security, the article indicates that the progressive institutionalization of Northeast Asian non-traditional security cooperation would exert influence on the interactions of ideas between the regional actors, and would play the role of intermediary in building regional security mechanism. In other words, the procedures are promoting the change of concept through partial practice, and then developing a mechanism or institution under the basis of interim practical experience. And after all, it will build the basic framework and specifications for construction of a truly regional security mechanism, and even security community in future.