In general, iron drugs should be stopped three days before ultrasonic colonoscopy. Pay attention to eating liquid or semi-liquid foods with low fiber and little residue, such as milk, bean products, fish, porridge, noodles, eggs, bananas, apples, melons and potatoes. If you defecate more than once a day, you can start a low-fiber and low-residue liquid diet two days before the examination. You should eat liquid food that is easy to digest and absorb in your diet the night before the examination, and start taking laxatives two hours after meals. You need to fast, eat no food and drink no water on the day of the exam. Avoid using narcotic drugs for ultrasonic colonoscopy, which may easily lead to suffocation of stomach contents after vomiting and endanger life.