If the lesion is located in the pouch, the intestine is not clean, the influence of abdominal breathing movement, and the presence of too fast retreat, colonoscopy is very easy to miss the diagnosis, especially for small flat polyps and tumor lesions in the colon can reach 15-20%, or even higher. Bowel preparation is crucial to improve the diagnosis of early colorectal polyps and tumors. Once the bowel preparation is inadequate, the doctor will describe your poor bowel preparation in the report at the end of the examination and recommend you to repeat the colonoscopy regularly. How do you know if you are getting a high quality bowel preparation after a bowel cleanse? When diarrhea occurs after oral bowel cleansing solution, it can be classified as good, better, poor and worse according to the nature of the stool coming out of the diarrhea, and obtaining good and better yellowish loose water stool can be considered as high quality bowel preparation. What are the criteria for high quality bowel preparation in the eyes of a doctor? (1) The Boston criteria used for colonoscopy are divided into four grades of bowel preparation: very good, good, fair, and poor, according to the clarity of the bowel lumen during colonoscopy. Very good and good are high quality bowel preparation. (2) The Ottawa standard is used for colonoscopy, which is divided into five levels: very good, good, average, poor and inadequate preparation according to the clarity of different parts of the intestinal cavity during colonoscopy, and a score of 0 or 1 is considered high quality bowel preparation. How to achieve high quality bowel preparation? (1) Abstain from eating red or multi-seeded foods, such as watermelon, tomatoes, kiwi, etc., two days before the examination, so as not to interfere with the colonoscopic observation. (2) Eat less residue semi-liquid food such as thin rice and noodles for lunch and dinner the day before the examination, and do not eat vegetables, fruits and other multi-residue foods and dairy products. (3) long-term constipation for various reasons 3-5 days before the examination should begin to make preparations, can take mosapride, trimethoprim and other power drugs; oral lactulose or magnesium sulfate and other laxative; before defecation can use cork, be sure to defecate at least once a day, the day before the colonoscopy is not defecated, that night can be taken in advance oral polyethylene glycol electrolyte solution 2 liters to induce diarrhea. (4) The standard bowel cleansing time is 2-3 liters of oral polyethylene glycol electrolyte solution more than 4-6 hours before the colonoscopy. If yellow dilute watery stool is not reached after oral administration, 1-2 liters of oral polyethylene glycol electrolyte solution can be added or clean enema can be performed until yellow clear stool. (5) When the stool is solved to dilute watery stool, add dimethylsilicone oil defoamer (5g + 50-60ml of warm water) or mucus proteolytic enzyme, etc. orally to remove mucus foam in the small intestine.