This is a clichéd topic, but the fact is that there are still many patients who cannot perform colonoscopy properly even due to unclean bowel, which once delayed the disease. Good intestinal cleanliness is the prerequisite and foundation to ensure the quality of colonoscopy treatment. What should be done? 1, dietary intervention Because coarse fiber food is not easy to be digested and excreted, three days before the examination, try to avoid eating coarse fiber vegetables (such as celery, leek, etc.); in addition, in order to avoid disturbing the field of view of the red, granular and other contents of the intestinal residue, two days before the examination, try not to eat red food (animal blood, tomatoes, red dates, etc.), seeded fruits (dragon fruit, kiwi watermelon, etc.). The day before the examination, semi-liquid diet, can eat noodles, thin rice, steamed buns, etc. The night before the examination, liquid and dregs-free diet, you can eat clear soup, honey water, white sugar water, etc.; dairy products (milk, soy milk, etc.) are prohibited. 6 hours before taking the purgative (see below for details of the time to take the purgative), you need to fast for more than 4-6 hours to ensure that there are no residual contents in the stomach and to ensure intestinal cleanliness. 6 hours before the examination, fasting and drinking, especially reminded that painless colonoscopists should not steal water under the pretext of laxative, so as not to accidentally enter the whistle during the examination. 2. Drug intervention ① Choice of drugs Polyethylene glycol electrolyte dispersion (PEG) is an isotonic solution that does not affect the absorption and secretion of the intestine, and its safety and effectiveness are recognized by the public, and it is the most commonly used intestinal cleanser in China. In addition to the above laxatives, senna and mannitol also have similar cleansing effects, but are poorly accepted by patients. ②Dosing amount and method of drugs According to the varieties and rules of different cleansers, different amounts of isotonic liquid are prepared. In general 137.15g of PEG drug is all dissolved in 2000ml of warm water (about 4 bottles of mineral water), stirred well and taken orally while walking, together with lightly rubbing the abdomen to accelerate intestinal peristalsis, and controlled to be drunk within 2 hours. People with constipation are better off taking the cleanser in divided doses in order to get the ideal cleansing of the intestines. ③ Time point for taking it For morning examination, start taking the cleanser at 6-7 pm the night before the examination day and finish it within 2 hours; for afternoon examination, start taking the cleanser at 8-9 am and finish it within 2 hours. After taking the cleanser, pay attention to the shape of the stool, until the discharge of clear water-like stool to complete the intestinal cleansing; if the clear water-like stool is not reached, you need to continue to drink 1000 ml of warm water to further cleanse the intestine.