Today, the mystery of security and the category of defense of the country, in parallel with the fundamental changes and developments in the international system and chaos in it, has faced special complications, and due to non-linear and irregular approaches and the variety of threats, defense policy making in the conditions of ambiguity and Uncertainty is placed. In this situation, how to adopt the desired defense policy is a fundamental issue. In line with this issue, the main question is, what model is suitable for designing and formulating defense policies in complex and chaotic international systems? In this research, an attempt has been made to analyze defens policy making by using the descriptive-analytical method and within the framework of the theory of complex and chaotic systems. The results of the research indicate that within the framework of the theory of complex and chaotic international systems, defense policymaking is influenced by the chaotic and crisis-producing components of this system and should be focused on non-linear and dynamic situations. In such situations, the application of the contingent or positive model in policy-making can be a suitable answer to the problem, because it tries to adopt the most suitable policy according to the environmental conditions and situations.