The purpose of this study is to provide informations regarding a definition, role, and methodology of the Net Assessment. Despite numerous quotations from academia and the policy community, and being widely known, little is known about the detailed methodology and content of the Net Assessment. Moreover, domestic academic research on it is not active yet. Not only has the methodology been studied, but the origin and development of the ONA(Office of Net Assessment) of US DoD has not been well introduced. Given that the Net Assessment is an analysis tool that has been used to analyze the long-term U.S. military Competition in the Cold War, we seem to need research at an academic and policy level as a tool to assess the military balance in the competition facing Korea. In this backdrop, the study analyzes the concepts and skills and historical application cases, and analyzes the key elements and principles of the Net Assessment.