Laxatives should be taken 4~6 hours in advance before doing colonoscopy, and drunk within 2 hours to fully empty the intestine until the stool finally shows a clear watery pattern, which makes the bowel ready for colonoscopy. The night before the colonoscopy, you need to eat light and easy to digest food, preferably fluid or semi-fluid food, fasting on the day of the colonoscopy, and take laxatives 4~6 hours in advance, take polyethylene glycol electrolyte bulk as an example, you need to dissolve a box of polyethylene glycol electrolyte bulk in 1000ml of water, a total of 3 boxes of 3,000ml of water, divided into 3~4 times to drink up within 2 hours, and appropriate exercise. When the patient finally discharges transparent watery stools, only then is the bowel preparation considered successful. On the day of the colonoscopy, if the patient feels hungry, he or she can only take colorless sugar cubes to keep up his or her strength. In addition, patients with anal fissure, perianal abscess, severe cardiopulmonary insufficiency, shock, abdominal aortic aneurysm, acute peritonitis, ulcerative colitis, intestinal perforation, intestinal stenosis, and pregnant women are prohibited from having colonoscopy. If you need to undergo colonoscopy, please follow the doctor’s instructions for treatment.