Abstract: The theory of natural law has suffered a serious inner crisis before the attack from legal positivism. It lays the foundation for the rise of legal positivism. This paper attempts to explore the inner logic of the theory of natural law with an analysis of the "nature" and "reason" of Hobbes' ideology from the perspective of evolution of ideas on nature from the ancient Greek to modern times. It also analyzes the argument of religion in Leviathan, revealing the disruptive strike against the basis of traditional theory of natural law. Accordingly it establishes Hobbes' status as the theory pioneer of legal positivism.