The precautions before doing colonoscopy mainly include diet, adequate intestinal preparation, and elimination of contraindications to surgery. 1. Diet: patients should pay attention to their diet three days before the colonoscopy, and try to focus on liquid or semi-liquid diet with little or no residue, such as millet porridge, egg custard, rotten noodles, etc. Avoid foods that are difficult to digest, such as barbecue, or foods that are rich in dietary fiber, such as celery. Fasting 6-8 hours before the examination, fasting on the day of the examination. 2. Bowel preparation: In order to have a clear vision during the examination, patients also need to keep the intestinal tract clean by taking laxatives (such as compound polyethylene glycol electrolyte bulk, etc.), and generally the contents of the intestinal tract should be completely discharged, and the stools should be watery and free of food residues. 3. Excluding contraindications to surgery: patients should also undergo coagulation function, blood biochemistry, electrocardiogram and other tests before colonoscopy to exclude contraindications such as severe cardiopulmonary failure, perforation of abdominal organs, pregnancy, coagulation disorders, etc. which are difficult to tolerate colonoscopy, so as to ensure the safety of patients during the examination. Patients should strictly follow the doctor’s instructions to prepare for the colonoscopy so as not to affect the results of the examination.