Subarachnoid hemorrhage (SAH) is a collective term for the sudden rupture of a cerebral blood vessel from various causes and the flow of blood into the subarachnoid space. It is not a disease, but a clinical manifestation of certain disorders. Subarachnoid hemorrhage is clinically classified into two categories: spontaneous and traumatic. The common cause of spontaneous subarachnoid hemorrhage is intracranial aneurysm, followed by cerebral (cremaster) vascular malformation. Other causes include arteriosclerosis, smog, stroke with brain tumor, hematologic disease, meningitis, and complications of anticoagulation therapy, but all are rare. The clinical presentation is often sudden onset with severe headache, nausea and vomiting, impaired consciousness, positive meningeal irritation signs, psychiatric symptoms and epilepsy. Cranial CT plain scan is currently the test of choice for the diagnosis of spontaneous subarachnoid hemorrhage. 64-row and higher CTA has high sensitivity and specificity for etiologic diagnosis. Cerebral angiography is the “gold standard” for the diagnosis of this disease, and it is currently advocated that cerebral angiography should be done early for early etiologic treatment. For aneurysmal aSAH, when the Hunt-Hess grade is ≤Ⅲ, early surgical clamping of the aneurysm or endovascular interventional embolization is often performed, while for grade IV and V, further treatment is required after the condition is stabilized. Endovascular interventional embolization has become the preferred treatment for most aneurysms because it does not require craniotomy and does not interfere with brain tissue.