Doing colonoscopy before bowel clearing called bowel preparation, before the examination need to be 6 hours in advance for intestinal preparation, after sufficient preparation for feasible colonoscopy. 1. Patients need to take oral laxative 6 hours before the examination, avoid bed rest after taking laxative, need to walk around, when the feces discharged is colorless or light yellow transparent watery stools, no fecal sludge, it indicates that the intestinal tract is well prepared. If the bowel preparation is unsatisfactory, inform the medical staff for further bowel treatment or make another appointment for colonoscopy. 2. If there is long-term constipation, it is recommended to have a liquid diet for 3~4 days before the examination, and prepare an extra packet of laxative during the bowel preparation, which can be supplemented with an additional dose 8 hours before the operation if the bowel preparation is not effective. If the bowel preparation is not effective, you can take additional laxatives 8 hours before the procedure.