A middle-aged male patient was admitted to the emergency room earlier this month. He came to our hospital for treatment of a fall injury to the back of his head. The head CT showed scattered subarachnoid hemorrhage in the skull, which was easily misdiagnosed as traumatic brain injury according to the previous thinking. In fact, there was a hidden fatal killer – cerebral aneurysm in the patient’s skull. After the consultation of brain surgery, the patient was immediately prepared for surgery, and neurointervention — total cerebral angiography was performed under intravenous general anesthesia on the same day in emergency. During the operation, it was confirmed that the doctor’s judgment was correct, and the patient fell because of the rupture and bleeding of an anterior cerebral traffic aneurysm, not bleeding from traumatic brain injury. After timely identification of the cause of the disease, the patient underwent intracranial aneurysm clamping surgery at the first time, and the patient recovered well after the surgery. Intracranial aneurysm is an abnormal bulge in the wall of an intracranial artery (non-tumorigenic), which is rarely detected before rupture because the aneurysm is usually small and does not cause clinical symptoms. Rupture of an aneurysm can cause serious pathological changes such as subarachnoid hemorrhage (SAH). The mortality rate of first-time rupture and hemorrhage is about 30-40%, and the mortality rate of re-rupture can be as high as 60%, and the disability rate of the survivors is very high. Timely diagnosis and treatment of intracranial aneurysm is very critical. This is another case of intracranial vascular lesion since the development of neurointervention in our hospital.