By way of receiving training as intern, sorting out clinical medical records, and reading medical classics, the author of the paper analyzes Professor Tan Yi's understanding of the etiology and pathogenesis of chronic nonspecific ulcerative colitis, summarizing his clinical experience in the treatment of this disease. Professor Tan Yi believes that deficiency of spleen and stomach, dampness and turbidity, and blockage of qi movement are of great significance in the pathogenesis of chronic nonspecific ulcerative colitis. It is suggested that the treatment at the early stage should be based on eliminating pathogenic factors, and the treatment of an enduring one be based on supplementing and boosting, warming and activating spleen qi. In the whole process, attention should be paid to distinguishing de fi ciency from excess, combining strengthening vital qi with eliminating pathogenic factors. As for diagnosis and medication, it is proposed that prescriptions be selected based on syndrome differentiation, making flexible adjustment in compatibility of medicines and their dosage, and making good use of classic and minor prescriptions.