Oral mannitol injection before gastroenteroscopy is mainly designed to help clean the intestinal tract and prepare the intestines for gastroenteroscopy. Because mannitol has a degree of hypertonic effect, it can promote gastrointestinal peristalsis and thus effectively play a role in cleansing the intestinal tract. It is recommended to do 4-8 hours before the colonoscopy, you can drink mannitol 500 ml – 1000 ml or so, generally after drinking it is recommended to moderate exercise, such as walking, about half an hour will slowly defecate, and during this time, pay attention to drink more water, do not eat food. The final discharge of stools is watery or pale yellow, without fecal sludge, for optimal intestinal cleansing. Adverse reactions such as electrolyte disorders, chills, fever, and difficulty urinating may occur with mannitol. Mannitol is contraindicated in patients with anuria, severe water loss, active intracranial hemorrhage, acute pulmonary edema, and severe pulmonary stasis. When using this drug, it is necessary to use it under the supervision of a doctor.