1, a lot of blood in the stool: blood in the stool is one of the main clinical manifestations of the disease, and the amount of blood in the stool is also an indicator of the severity of the disease, but sometimes it is difficult to quantify absolutely. 2, intestinal stricture: mostly occurs in cases with extensive lesions and persistent disease duration of more than 5-25 years, and its site mostly occurs in the left hemicolectomy, sigmoid colon or rectum. The reason is the thickening of the mucosal muscle layer or the blockage of the intestinal lumen by pseudo-polyps in clusters. 3.Intestinal perforation: It is mostly a complication of toxic intestinal dilatation, but can also occur in severe type. The application of corticosteroids is considered to be a risk factor for intestinal perforation. 4.Toxic intestinal dilatation: clinical manifestations are highly dilated intestinal canal with toxic symptoms, obvious distension in the abdomen, the most obvious dilatation site in the transverse colon, physical examination of the abdomen may have pressure pain or even rebound pain, intestinal sounds significantly weakened or disappeared. 5, colon cancer: it has been recognized that the chance of ulcerative colitis complicating colon cancer is significantly higher than the general population of the same age and sex group, it is generally believed that the trend of cancer and the length of the disease, after 15-20 years of disease, the risk of cancer increases by about 1% per year. 6, polyps: the incidence of 10% to 80%, often called these polyps as pseudopolyps. 7, internal fistula: intestinal cavity and intestinal cavity or intestinal cavity and other cavity organs (such as bladder, vagina, etc.) adhere to each other, forming an internal fistula; intestinal cavity and skin to form an external fistula, although less often, but occasionally occur. 8, anal and perianal diseases: such as anal fissure, perirectal abscess, anal fistula, hemorrhoid prolapse, etc. 9, other systemic complications such as non-specific arthritis, erythema nodosum, gangrenous pyoderma, iritis, iridocyclitis, keratitis, stomatitis and mumps, as well as fatty liver, small bile duct periarthritis, etc.