Before doing colonoscopy, patients need to clean up their intestines, because a clean intestinal environment helps to accomplish high-quality intestinal examination and treatment. 1. Three days before the colonoscopy, pay attention to adjust the diet structure, light, less residue diet, 8 hours before the colonoscopy need to fast, colonoscopy 4 to 6 hours before the oral intestinal purging medication, so that the feces discharged is clear water. 2. Clean intestinal lumen helps doctors to operate and reduce patients’ discomfort; it helps to expose the field of vision and avoid feces covering the mucous membrane, which affects the doctor’s judgment and thus reduces the occurrence of misdiagnosis and omission; it helps to implement the treatment and reduces the risk of bleeding and contamination. Intestinal cleanliness is closely related to the diagnostic and therapeutic effects of colonoscopy. It is recommended to follow the doctor’s instructions for adequate bowel preparation to avoid missing lesions or delaying treatment.