Mannitol is a common drug used in neurology, mainly as an osmotic dehydration drug to treat conditions such as cerebral edema and increased intracranial pressure. While cerebral edema is mostly caused by trauma, cerebral infarction and cerebral hemorrhage, mannitol is also one of the drugs of choice for the treatment of these diseases. The usage of mannitol can be used alone or in combination with diuretics. Mannitol alone, mainly 20% mannitol is administered intravenously every 4-12 hours or every 8-12 hours, 250 ml at a time, up to 500 ml, or 125 ml for the elderly. Mannitol is very effective and takes effect in about half an hour after the drip, and has a significant effect on reducing intracranial pressure. Mannitol also has side effects, mainly a drop in blood pressure and a certain effect on kidney function. If a patient is in shock or has renal insufficiency, mannitol should be used with caution.