The term Horner syndrome refers to a characteristic group of ocular symptoms caused by damage to the vegetative nerves, mainly the sympathetic ganglion of the neck, among others. The disease can occur with damage to any segment of the cervical sympathetic pathway. It is rare for the disease to be caused by a lesion of the central nervous system above the 1st thoracic medulla. The disease is very dangerous to the physical and mental health of patients, so we need to know more about the causes of Horner’s syndrome in daily life and prevent it early. The causes of Horner’s syndrome include injury and compression of sympathetic nerves in the neck and brain cadres, such as trauma, surgery, tumors, inflammation, and vascular lesions. Inflammation, tumor compression, and hemorrhage in the inferior optic thalamus, brainstem, carotid medulla, and carotid artery can also cause the sympathetic nerves to be compressed, and a few cases can be congenital or have no obvious cause. The pathogenesis of Horner’s syndrome can be caused by the stimulation of sympathetic nerve, which can produce the symptoms of pupil dilation, lid widening, eye protrusion, vasoconstriction and excessive sweating on the head and face, so when there is any part of the pathway from sympathetic nerve center to eye and face with the above mentioned causes, the opposite manifestation will appear.