E-colonoscopy is the preferred instrument and gold standard for diagnosing colorectal diseases, especially colorectal cancer and related precancerous diseases. It transmits the image of colon mucosa to the electronic computer processing center through the electronic camera lens installed in the front of the colonoscope, and then displays it on the monitor screen. Through the display screen, the subtle changes of colon mucosa such as inflammation, erosion, ulcer, bleeding, pigmentation, polyp, cancer, hemangioma, diverticulum, submucosal lesion, etc. can be clearly observed, and the image is clear and realistic. In addition, biopsy forceps can be fed through the instrument channel of colonoscopy to remove rice-sized tissues for pathological sectioning to determine the nature of lesions, and also for microscopic polyp treatment, hemostasis, localization of lesion markers, and special staining treatment. Indications for colonoscopy: 1) unexplained diarrhea, abdominal pain, blood in stool, black stool, positive occult blood in stool, change in stool habit, abdominal mass, wasting, anemia, suspected lesions in colon, rectum and terminal ileum; 2) barium enema reveals lesions such as stenosis, ulcer, polyp, carcinoma, diverticulum, etc. in the intestinal cavity, which must be biopsied to further clarify the nature of lesions; 3) metastatic adenocarcinoma, searching for the primary lesion; 4) ulcerative colorectal cancer, which can be treated by microscopic polyp treatment, hemostasis, localization of foci, special staining, etc. 4.Diagnosis and follow-up of ulcerative colitis, Crohn’s disease, etc.; 5.Treatment of hemostasis and polyp removal 6.Census of high-risk group of colorectal cancer 7 Post-operative review of colorectal cancer and colorectal polyps, etc. Contraindications for colonoscopy: 1.severe anal and rectal stenosis, perianal abscess, anal fissure; 2.acute severe colitis, severe radiation enteritis; 3.extensive intra-abdominal adhesions; 4.advanced cancer with extensive intra-abdominal metastases; 5.acute diffuse peritonitis; 6.severe ascites, pregnant women; 7.severe cardiopulmonary failure, severe hypertension, cerebrovascular disease, mental abnormalities and coma patients . Intestinal preparation before colonoscopy: 1. Do not eat fiber-rich fruits and vegetables the day before the examination, and fast on the day of the examination; 2. There are many methods of intestinal cleansing, and each hospital uses different medications. Intestinal preparation should be performed according to medical advice (especially for those who perform painless colonoscopy). For those who take oral medication to cleanse the intestine, drink more water after taking medication, and finally discharge stools in clear water or light yellow, without fecal residue, for the best intestinal cleaning effect. Colonoscopy precautions: 1, after taking the drug, if the discharge contains feces or fecal water-like liquid, you should promptly tell the colonoscopy medical staff for further intestinal treatment. 2, in order to facilitate the entry of the mirror or see the mucosal pattern of the intestinal cavity, doctors sometimes need to inject a small amount of air into the intestinal cavity to expand or expose the intestinal cavity, at this time, patients often feel bloated and have the feeling of relieving stool; in addition, due to the curved and tortuous large intestine, sometimes the bending angle of the intestine is too large, or the patient has a history of abdominal surgery, intestinal adhesions, colonoscopy in the passage, the patient will feel some distension and pain. At this time, it is best to take a deep breath and not to overstress, otherwise intestinal spasm is likely to occur, increasing the difficulty and risk of the doctor into the mirror and prolonging the operation time. 3, the average colonoscopy takes about 15 minutes, sometimes due to individual differences, or abnormalities in the large intestine, the examination time may be a little longer. 4.There are certain risks in the colonoscopy, for your safety, ECG should be performed for the elderly over 60 years old. 5.If you have obvious abdominal pain, bloating, dizziness and other symptoms after the intestinal examination, you should tell your doctor in time for further treatment.