1, long-term blood in the stool, positive occult blood in the stool, especially dark red blood stool, consider the location of the lesion in the colon or rectum. 2, repeated diarrhea, constipation, especially with mucus-pus-blood stool. 3, abdominal masses, especially lower abdominal masses or with unexplained wasting, anemia, suspected intestinal disease, need a clear diagnosis. 4.Sudden change in stool habit or difficulty in defecation. 5, gas barium enema or gastrointestinal imaging found abnormal, need to further examine the colon or clarify the nature of the lesion. 6.Colon lesions have been found, but the diagnosis is not clear enough, or endoscopic treatment is needed, trans-colonoscopy and treatment should be considered. 7.Past history of colorectal polyps or tumors, which have undergone colonic luminal surgery, laser treatment, or colorectal resection, should be reviewed in six months to one year according to the medical history. 8.Colorectal cancer high incidence area, elderly people and people with family history of colorectal tumor who have intestinal symptoms should be censored. 9.Schistosomiasis is highly suspected, and multiple stool examinations are negative. 10.History of pulmonary tuberculosis with change in stool symptoms needs to exclude intestinal tuberculosis. 11, sigmoidoscopy does not find lesions or the nature of lesions is not known, fiber colonoscopy can be done.