The international norm is one of the major topics in international relations research, of which synthesized approach is gradually becoming a trend. This paper attempts to adapt Frank Schimmelfennig's approach-the strategic actions in an international norm community-to synthesize the theories of rationalism and constructivism in the international norm circle. As the case, the Proliferation Security Initiative will be analyzed through different phases of emergence of the life circle-cascade, diffusion, internalization, and erosion-to understand the motives of the participant states. For presenting the synthesized approach, various aspects of understanding can be provided.