A low-fiber diet needs to be started 1-3 days in advance before having a colonoscopy, and a medication such as polyethylene glycol needs to be used to clean the intestines the day before the test. 1. Dietary preparation: 1-3 days before the colonoscopy you need to start a low-fiber diet, you can eat white porridge, noodles, etc. Avoid eating fruits, vegetables, whole grain cereals and excessive meat. Avoid excessive intestinal secretions to affect the test results. 2. Drug preparation: According to different hospitals, different drugs are used before colonoscopy, mainly including mannitol, polyethylene glycol, magnesium sulfate, etc. Through the effect of drugs to discharge the intestinal feces and residual food, to achieve the purpose of intestinal cleansing to avoid interfering with the endoscopic field of view. Good bowel preparation can improve the accuracy of colonoscopy, and it is recommended to follow the medical advice to complete the preparation before colonoscopy.