Laxatives can be started 4 to 6 hours before the colonoscopy. Colonoscopy is one of the most direct and effective ways to check intestinal diseases, including colonoscopy and small bowel examination, of which colonoscopy is more commonly used. In colonoscopy before the need to fully prepare the intestinal tract, in the examination of 4 ~ 6 hours before the start taking laxatives, such as polyethylene glycol electrolyte bulk, etc., to empty the feces in the intestinal tract, so that the discharged material is watery and no fecal sludge can be. Constipated patients need to follow the doctor’s instructions to take medication in advance for intestinal preparation. In addition, before the colonoscopy need to fasting 6~8 hours, the day before the examination is recommended to eat low fiber, no slag food. Patients who need to undergo colonoscopy should fully prepare their intestines and cooperate with the doctor’s examination process.