The preparation before colonoscopy is mainly to clean the intestines, including fasting, taking laxatives, eliminating intestinal foam, and the precautions are to exclude contraindications to the procedure. 1. Fasting: A light diet is recommended two days before the colonoscopy, and semi-fluid food is preferred. The night before the colonoscopy, usually after 6 o’clock fasting. At the same time, appropriate water, if necessary, intravenous energy. 2. Taking laxatives: Start bowel preparation the night before the colonoscopy. Oral medication, such as compound polyethylene glycol, is taken 6 to 8 hours before the examination to promote the discharge of food residue in the intestines, while fasting and drinking a lot of water until the discharge of food residue-free stools. The drug can cause vomiting, shock; intestinal obstruction, intestinal perforation is prohibited. 3. Elimination of intestinal foam: Oral dimethylsilicone oil is taken 1~2 hours before the start of colonoscopy to eliminate the foam in the intestinal tract to improve the vision and clean the intestinal tract in the process of colonoscopy, which will help to get more accurate results and avoid polyps and tumors from being missed. Allergies are prohibited. 4. Excluding contraindications to surgery: perfect coagulation function, blood routine, blood biochemistry, blood infectious diseases and electrocardiogram and other tests to exclude contraindications to surgery, such as severe cardiorespiratory failure, acute diffuse peritonitis, perforation of the abdominal cavity, women in pregnancy, and discontinue the use of drugs affecting the coagulation function. Before colonoscopy, patients are advised to make preparations such as fasting, taking laxatives, eliminating intestinal foam, etc. under the guidance of the doctor to rule out contraindications to the procedure, so as not to affect the results of the examination or cause other discomforts.