Colonoscopy is the main method of diagnosing intestinal diseases, which can observe the whole colon under direct vision, such as polyps, ulcers, inflammation, bleeding location, tumor lesions, and perform resection if necessary. Usually the following conditions need to do colonoscopy: 1, unexplained lower gastrointestinal bleeding; 2, chronic diarrhea, chronic constipation, bowel movement abnormalities, defecation habit changes in patients; 3, fecal occult blood positive, abnormal tumor markers, anemia, imaging studies suspect that there are intestinal pathology of patients; 4, unexplained low intestinal obstruction; 5, inflammatory bowel disease need to do to differentiate and diagnose the extent of the scope of the involvement and degree of 6, colorectal polyps or early stage of bleeding, tumor, and the need for removal of the colonoscopy. Removal of colorectal polyps or early cancer; 7. Removal of intestinal foreign bodies; 8. Regular postoperative review for patients with intestinal polyps and colorectal cancer; 9. People with high risk factors for colorectal cancer, including colorectal polyps, familial polyps and polyposis, inflammatory bowel disease (including ulcerative colitis and Crohn’s disease), post cholecystectomy, and people with a family history of colorectal cancer; 10. People with long-term mental depression; 11. People who have not yet completed the first colonoscopy at the age of 50. first colonoscopy. Is colonoscopy appropriate at any time? Not really! Colonoscopy is prohibited in the following cases: 1. Severe cardiopulmonary insufficiency; 2. Severe hypertension, obvious cardiac arrhythmia, insufficient cerebral blood supply; 3. Acute gastrointestinal hemorrhage, intestinal blood accumulation, or excessive accumulation of blood that prevents observation; 4. Recently underwent surgery and radiation therapy for the gastrointestinal tract or pelvic cavity; 5. Intra-abdominal adhesion due to surgery and inflammation; 6. Anal stenosis and acute inflammation of the anus; 7, Stenosis of the intestinal tract; 8. Female pregnancy and menstruation; 9. Psychiatric patients or those who cannot cooperate.