The average time for a colonoscopy is 15 minutes, sometimes it may take a little longer depending on the person or if there is an abnormality in the colon. Also bowel preparation takes time. In order to perform a colonoscopy safely and accurately, cleansing of the colon needs to be completed before the colonoscopy. If the colonoscope is operated in a bowel full of feces, it is easy to cause unnecessary injuries, or the endoscopist will not be able to exert the force correctly due to fecal obstruction of the bowel lumen; also due to the fecal obstruction, it is necessary to flush it out before continuing to complete the examination, which will delay the time of the examination. Insufficient cleaning before colonoscopy is time-consuming, laborious and unsafe. Generally speaking, 2-3 days before the examination, eat less slag semi-liquid diet, such as thin rice, do not eat multi-fiber vegetables, fruits, forbidden to eat red or multi-seeded food, such as watermelon, tomatoes and so on. 1 day before the examination, eat non-dregs of liquid food, such as rice soup, no milk. On the day of examination, breakfast is forbidden for the morning examination, and breakfast is liquid and lunch is forbidden for the afternoon examination. Take laxatives 4-6 hours before the colonoscopy and discharge colorless dilute watery stool before completing the bowel preparation. Colonoscopy is divided into ordinary colonoscopy and painless colonoscopy. Painless colonoscopy is a colonoscopy performed under general anesthesia, in which the doctor helps you to quickly fall asleep without feeling the bloating and pain caused by colonoscopy. Although painless colonoscopy can reduce the pain, it is also impossible to give any feedback to the doctor’s operation during the examination, so the risk of painless colonoscopy operation is slightly higher than that of ordinary colonoscopy, and the cost is also relatively high. The choice of the examination method and the length of the examination also varies from person to person, and patients can make appropriate choices according to their own tolerance and underlying diseases.