I. Indications for colonoscopy: 1. Blood in the stool of unknown origin. 2. Chronic diarrhea of unknown origin. 3.Unexplained abdominal mass, cannot exclude large intestine and ileal end lesions. 4.Unexplained pain in the lower and middle abdomen. 5.Suspected benign or malignant colon tumor, which cannot be diagnosed by X-ray examination. 6.Suspected chronic intestinal inflammatory disease. 7.Abnormalities are found in barium enema or intestinal system examination, and the nature and scope of lesions need to be further clarified. 8.Determine the scope of lesions before surgery for colon cancer, postoperative review and follow-up of the efficacy of colon cancer and polyps. 9.Low-grade intestinal obstruction of unknown origin. Preparation before colonoscopy: 1, routine check hepatitis B five items, suspected polyp patients plus check coagulation four items, elderly patients plus check electrocardiogram. 2, the day before the examination into a semi-liquid diet with less residue, no vegetables and fruits and meat. 3.Patients with constipation, please take oral laxatives such as phenolphthalein tablets and Panaxia tea 2-3 days in advance to induce diarrhea and ensure that the intestines are clear one day before the examination. 4.Intestinal cleanliness on the day of examination: fast in the morning of the day of examination (Tuesday), take polyethylene glycol electrolyte or sodium phosphate oral solution plus enema before examination to cleanse the intestine fully. The usage of polyethylene glycol electrolyte is to start drinking at 7:00 am on an empty stomach, 2 large packets + 2 small packets with warm water 250ml, drink a glass of water every 15 minutes after drinking, and keep drinking all 4 large boxes, about 3000ml; sodium phosphate oral solution is also to start drinking at 7:00 am on an empty stomach, 45ml (a J) plus 750ml of warm water dilution, drink warm water after drinking, drink at least 2000ml of water in total. 2000ml of water, before the colonoscopy and then enema with sodium phosphate enema solution. 5, to ensure the completion of intestinal cleansing, a small amount of food at noon, drink some thin rice, noodles, eggs and so on, do not eat vegetables, fruits with seeds, etc..