Except for special cases of emergencies, patients need good bowel preparation before performing abdominal CT examinations. Good intestinal preparation can reduce the difficulty of diagnosis and improve the accuracy of diagnosis. Bowel preparation is as follows: 1. 5-8 hours of fasting: Patients are usually required to stop eating after 23:00 pm the night before the examination and can drink liquid food; 2. 15-20 minutes before the examination: Patients need to drink 500 ml of water 15 minutes before the examination; 3. Before getting on the examination bed: Patients should drink another 200-300 ml of water after entering the examination room and before getting on the examination bed. If patients do small intestine CT then they need to be guided or enema, after emptying all the contents of the gastrointestinal tract, drink 2000ml of water to fill up the gastrointestinal tract, and use drugs to inhibit intestinal peristalsis half an hour before the examination.