Colonoscopy is a common examination method among the digestive system, which can clearly understand the size, shape and distribution characteristics of intestinal lesions, and is one of the most common means of diagnosing and treating colorectal diseases. The corresponding colonoscopy should be performed when the following conditions are met: 1. change in bowel habits: significant diarrhea or constipation within a short period of time, too many or too few stools, which may be caused by intestinal inflammation, intestinal polyps, intestinal tumors; 2. abdominal pain: mostly manifested as chronic hidden pain, distension or colic in the lower and middle abdomen, not relieved by the application of drugs; 3. pus and blood stool: refers to the stool mixed with pus-like material and blood. Gastroscopy and colonoscopy should be done to clarify the cause and location of bleeding. 4. change in stool characteristics: difficult defecation, urgency or too thin, too flat stool. 5. bloody stool: anemia with positive fecal occult blood should be examined by gastroscopy. 6. those who need to be reviewed after treatment of previous intestinal diseases. 7. those who need endoscopy for intestinal diseases. In addition to the above symptoms, if there is a family history of colorectal cancer, especially for people over 40 years old, even if there are no symptoms, they need to have regular colonoscopy every year. Because most bowel cancers evolve from intestinal polyps, which do not have symptoms such as change in stool shape and abdominal pain in early stage, patients may not have any discomfort in early stage, so early screening is needed.