The main use of mannitol is intravenous drip, for intestinal preparation need to be taken orally. There are many precautions for mannitol, which should be used with caution in patients suffering from some diseases and should be used in strict compliance with medical advice. Mannitol is used intravenously to lower intracranial pressure, lower intraocular pressure, prevent acute tubular necrosis, drug poisoning and other aspects; if it is used for preoperative bowel preparation, it needs to be taken orally. There are many precautions for mannitol, different diseases, age and weight, the concentration and dose of mannitol used is not the same, patients with obvious cardiopulmonary impairment, hyperkalemia, hyponatremia, hypovolemia, severe renal failure and other diseases should be used with caution. In addition pregnant women, lactating women, children, the elderly and other groups of people should also be careful with the drug. Blood pressure, renal function, blood electrolyte concentration, and urine output should be followed up during use. The use of mannitol may produce adverse reactions, such as water and electrolyte disorders, chills, fever, tissue edema, dizziness and so on. The method of use and precautions should strictly refer to the instruction manual, and strictly follow the doctor’s instructions to use the drug.