The adaptation of colonoscopy is very broad, and anyone who is willing to undergo colonoscopy without contraindications can undergo colonoscopy. The following conditions should be done early: 1. unexplained gastrointestinal bleeding, including blood in the stool or positive fecal occult blood; 2. unexplained chronic diarrhea, constipation or a sense of incomplete defecation; 3. unexplained pain in the lower and middle abdomen, especially when it gradually worsens; 4. unexplained extreme fatigue, weight loss or anemia; 5. unexplained abdominal masses, suspected of lesions in the large intestine or the end of the ileum 6, unexplained low intestinal obstruction; 7, suspected benign or malignant colorectal tumor; 8, suspected inflammatory bowel disease such as ulcerative colitis, Crohn’s disease; 9, barium enema found abnormal, need further clear diagnosis; 10, colorectal cancer before surgery to determine the extent of the lesion; 11, regular review and efficacy follow-up after colorectal surgery and colonoscopy; 12, colorectal polyps, tumors, bleeding and other lesions Need for colonoscopic treatment; 13. Screening of colorectal tumors, especially when the blood test carcinoembryonic antigen is abnormally elevated.