Sudden headache with splitting should first be considered as subarachnoid hemorrhage and cerebral hemorrhage. Subarachnoid hemorrhage is a stroke with corresponding clinical symptoms caused by blood flowing into the subarachnoid space after rupture of blood vessels at the base or surface of the brain, also known as primary subarachnoid hemorrhage, accounting for 5%-10% of all strokes. The etiology of the disease mainly includes intracranial aneurysms, which account for 50%-85%, cerebrovascular malformations, which account for about 2%, and anomalous vascular network at the base of the brain, which account for 1%. Other etiologies include entrapment aneurysms, vasculitis, intracranial venous system thrombosis, hematologic disorders, intracranial tumors, and others. The main manifestation of the disease is sudden onset of severe headache with swelling and explosion-like pain, which is unbearable and can be confined to the whole headache, and sometimes the pain can also appear in the upper cervical segment, which cannot be relieved or aggravated progressively. Patients are often accompanied by nausea and vomiting, and can have disturbance of consciousness or mental symptoms such as irritability, delirium, hallucinations, etc. A few patients can have partial and full-blown seizures, and can also have dizziness, vertigo, etc. It is recommended to check the cranial CT at the hospital to further clarify the diagnosis and treatment.