Preparation before having colonoscopy includes diet adjustment, bowel cleansing, blood tests and examination and evaluation. 1. Adjustment of diet: Before having colonoscopy, diet should be adjusted three days in advance, for example, the food should be light, soft and easy to digest, and vegetables and fruits containing more fiber should be forbidden. Try not to eat watermelon, tomatoes and other foods with special color, fasting on the day of colonoscopy, keep fasting, so as not to affect the examination. 2. Clean up the intestinal tract: the day before and on the day of colonoscopy, you should take diarrhea-inducing drugs under the guidance of a professional doctor, such as compound polyethylene glycol electrolyte dispersions, and at the same time, drink a lot of water to promote excretion, and clean up the residual food residues in the intestinal tract. 3. Blood test and examination and evaluation: Before doing colonoscopy, blood test should be done, mainly checking blood routine, coagulation function and serum four. If the elderly do colonoscopy, they should do electrocardiogram, cardiac ultrasound as well as chest X-ray for cardiopulmonary function assessment. If you need to do a colonoscopy, you must be examined in a regular hospital, and communicate in detail with a professional doctor to understand clearly the attention and preparations before the examination, so as to be well-prepared for the examination.