The causes of diarrhea in ulcerative colitis are multifaceted and have not yet been fully understood. In summary, it may be related to the following causes: 1. impaired absorption and secretion of water and electrolytes in the inflamed colon. 2, into the colon of fat, sugar by bacterial decomposition or produce excessive bile salt products, etc.. 3, the colon’s sodium retention function and rectal contraction function are reduced during inflammation. 4.Laxogenic effect of bacterial enterotoxins when secondary intestinal infection occurs. 5, Dysfunction of the colonic motive plant nervous system.