This paper develops its argument in three stages. First, we outline the root of Chang Tsai's theory of Li. For Chang Tsai, the way of nature is the metaphysical basis of Li, and Li is the concrete display of the principle of nature. Secondly, we discuss the ends of Li in Chang Tsai's philosophy. In Chang Tsai's thought, the Li is not only the rules of human behavior, but also the way in which the sage can put the community in order. Finally, we explore the moral practice of Li in Chang Tsai's philosophy. Chang Tsai stresses the activism of Li, which he believes is the way of man should be conjunct with the way of heaven. Through this three-stage study, we hope to reveal the rich contents of Chang Tsai's thought.