It refers to a clinical syndrome caused by the rupture of diseased blood vessels at the base or surface of the brain and the direct flow of blood into the subarachnoid space, also known as primary subarachnoid hemorrhage, which accounts for about 10% of acute strokes and is a very serious and common disease. The most common cause of spontaneous subarachnoid hemorrhage is rupture of intracranial aneurysm, followed by bleeding due to arteriovenous malformation; the onset may be preceded by triggering factors such as forceful defecation, coughing, violent mood swings, lifting heavy objects, strenuous exercise, and sexual intercourse, with variable onset and followed by severe headache, often described by the patient as the worst headache ever, feeling like the head is going to explode, often accompanied by nausea and even vomiting. In severe cases, there can be impaired consciousness, manifested as drowsiness, but waking up is possible, or coma, or even deep coma when the bleeding is large. Cold weather is the peak time for the onset of spontaneous subarachnoid hemorrhage. The symptoms of patients after subarachnoid hemorrhage (arachnoid hemorrhage) vary in severity, with most patients complaining of sudden explosive headaches. Early diagnosis of the cause of arachnoid hemorrhage and the presence of intracranial vascular lesions is the first step in treatment. Arachnoid etiology: ruptured intracranial aneurysm bleeding (80-90%), others include arteriovenous malformation, smoker’s disease, pericentral pool arachnoid blood and arachnoid negative. Imaging: CT scan of the head is preferred for the diagnosis of arachnoid hemorrhage. However, negative CT cannot exclude arachnoid hemorrhage because of the following reasons: prolonged time from onset to CT examination, small amount of arachnoid hemorrhage, low resolution of CT, etc. At this time, lumbar puncture is the appropriate choice. Intracranial aneurysm treatment: 1. Interventional treatment is preferred; 2. Cranial clamping is second choice; for a few cases where interventional treatment is not possible, only cranial clamping treatment can be chosen. Once the diagnosis is clear, etiological treatment needs to be carried out as early as possible to avoid life-threatening secondary hemorrhage.