Water accounts for about 80% of the brain, and water molecules flow between the cells in the brain, producing important physiological functions. At the same time, disorders of water metabolism in the brain can lead to the production and deterioration of the disease. With the continuous metabolism and circulation of water, various harmful substances produced by brain tissue will be taken away to maintain the internal environment of the brain. Studies have found that brain water metabolism is related to many types of diseases in clinical work, such as the occurrence of hydrocephalus caused by the direct increase of Cerebrospinal Fluid (CSF), as well as the early cell edema and late vasogenic edema caused by cerebral hemorrhage, cerebral infarction and other diseases. Changes in water metabolism caused by various causes will lead to an increase in intracranial pressure, resulting in compression and perfusion changes in brain tissue, and eventually lead to the deterioration of the disease. Cell edema in the brain, choroid plexus secretion and even the now popular spontaneous purification system of the brain has an important relationship with water metabolism. However, because we are not clear about the mechanism of controlling brain water transport, there is no effective targeted drug treatment for these conditions. This paper will discuss the various mechanisms of brain water metabolism.