After a cerebral hemorrhage, if the pupil is dilated and is not corrected in time, the patient often dies within 2-3 days. When the hemispheric hemorrhage is large, the pupil may be dilated because the hemorrhage presses on the parasympathetic fibers of the arterial nerve. Clinically, this sign is called brain herniation. After the occurrence of brain hernia, the brain tissue is squeezed and displaced, which in turn presses the respiratory and heartbeat centers of the brainstem, and eventually leads to respiratory and circulatory failure and death. Therefore, after cerebral hemorrhage, dehydration, cranial pressure-lowering drugs or surgical treatment should be given in time to remove the blood in order to avoid the occurrence of cerebral herniation, so as to save the patient’s life.