Before colonoscopy is mainly through oral polyethylene glycol electrolyte dispersion, magnesium sulfate, etc., and at the same time with drinking about 1500-3000ml of water to achieve the effect of cleaning the intestines, if you really can not finish drinking laxatives before doing colonoscopy, you can take laxatives on the basis of moderate reduction of water intake, or just take it orally in parts, if really when you can not drink, you need to clean the intestines by way of enema. When the intestinal tract is not cleaned, after the colonoscope goes down, the stool will obscure the intestinal tract, affecting the examination effect and preventing timely detection of the lesion site, resulting in the need to make another appointment for examination and clean the intestinal tract with medicine; or delaying treatment or even possibly worsening the disease because the lesion site cannot be detected in time during the examination. Therefore, when patients cannot tolerate it, they should not give up the medication or reduce the amount of laxatives at will, but can communicate with the doctor and change to other methods of bowel cleansing. In addition to bowel preparation, patients should not eat red, multi-seeded foods such as watermelon, tomatoes, kiwi, etc. two days before the examination so as not to interfere with the colonoscopy observation. 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. A small amount of snacks and chocolates can be prepared for consumption at the end of the colonoscopy. People with chronic constipation should explain to the doctor in advance, and 3 days before the examination, they can take motility drugs such as mosapride as prescribed by the doctor, and apply corky to stimulate defecation or take a small amount of lactulose or a small dose of magnesium sulfate solution to ensure that they have at least one bowel movement per day.