Pupillary changes in patients with brain herniation vary clinically, mainly in terms of pupil size. There are three types of herniation: cerebellar herniation, occipital foramen magnum herniation, and subfalx herniation, and the corresponding pupillary changes are as follows: 1. Cerebellar herniation: In the early stages of the disease, the stimulation of the articulatory nerve on the affected side causes the pupil to become smaller and the reflex to light to become dull. During the exacerbation of the disease, the articulatory nerve on the affected side may become paralyzed, the pupil gradually dilates, and the light reflex disappears. In the worsening phase, the pupils become dilated bilaterally, and the patient is in a state of near death. In addition, some patients may have abnormalities such as exophthalmos or ptosis in the affected eye. 2. Foramen magnum herniation: the brainstem tissue may be compressed, and the main risk for the patient is respiratory arrest, and the pupils may be large or small at the onset of the disease. 3. Subfalcate herniation: the pupils of the patient usually do not change abnormally, and the symptoms are mainly paralysis of the contralateral lower limbs, urinary disturbance or hyposensitivity. If the late stage of brain herniation causes severe coma and near-death symptoms, all of them will manifest as bilateral pupil dilatation and fixation. In summary, brain herniation is a clinically dangerous and critical condition that requires early human intervention. Currently, the critical period for brain herniation treatment is before the onset of the disease, while after it occurs, it should be treated medically or surgically to reduce the damage to the patient’s brain neurological function and save his life.