This paper summarizes the clinical experience of Professor Li Diangui, a Chinese medicine master,in differentiating and treating ulcerative colitis by stages based on the theory of resolving turbidity and detoxifying,gives a detailed introduction to the theory of turbidity and toxin, and tries to analyze the etiology and pathogenesis of ulcerative colitis from the perspective of turbidity and toxin doctrine. Professor Li Diangui’s clinical experience is summarized as differentiating treating ulcerative colitis by stages and making out proper prescriptions.