Mannitol mainly has tissue dehydration and diuretic effects. First of all, it has the effect of tissue dehydration, which can increase the plasma osmolarity and cause the water in tissues to enter the blood vessels, including the eye, brain and cerebrospinal fluid, thus reducing the edema of tissues, which can reduce the intraocular pressure, intracranial pressure and cerebrospinal fluid volume and pressure. Early on, it can increase blood volume and promote prostaglandin secretion, which dilates renal blood vessels and increases renal blood flow, including blood flow in the renal medulla, dilation of small glomerular inlet arteries, increased glomerular capillary pressure, and increased cortical glomerular filtration rate. However, mannitol is a monosaccharide, which is not metabolized in the body and is rarely reabsorbed in the renal tubules after glomerular filtration, playing an osmotic diuretic role. In clinical practice, mannitol is mainly used as tissue dehydration for cerebral edema caused by various reasons, to lower intracranial pressure and prevent brain herniation, and can also effectively lower intraocular pressure. It is used for treatment when other lowering of intraocular pressure is ineffective and in preparation for intraocular surgery. It is also used as an osmotic diuretic and as an adjunctive diuretic measure in the treatment of nephrotic syndrome and cirrhotic ascites, especially when the patient has hypoproteinemia. In addition, it can also provide relief for overdose or poisoning of certain drugs, and can facilitate the excretion of poisoned drugs.