Abstract: Locke's theory of natural law is a focal point of attention among modern western scholars. In contrast to some who understand Locke's theory mainly in virtue of the preservation of individuals and mankind, this paper turns to the early work of Locke, Essay on the Natural Law, and makes a clarification from three aspects, namely the essence of natural law, the acquisition of the knowledge of natural law, and the relation between natural law and positive law. Thus we can get a clear understanding of the profundity and complexity of Locke'theory.