Cyanosis or necrosis of the fingers is an ischemic symptom of the upper extremity in the clinical manifestations of subclavian artery steal syndrome: intermittent dyskinesia, upper extremity weakness, pain and abnormal sensation are the common ones, and rarely cause cyanosis or necrosis of the fingers. The preliminary diagnosis can be made based on the typical clinical symptoms, significant weakening or disappearance of radial artery ergitation, audible systolic vascular murmur in the supraclavicular fossa and systolic blood pressure significantly lower than the contralateral side. The following are the examination items: 1, transcranial Doppler ultrasound (TCD): detection of cervical blood vessels and blood flow, the reverse flow signal of the vertebral artery can be seen, and the affected side of the bundle arm test should be performed if the diagnosis is suspected. 2, color Doppler ultrasound: the beginning of the subclavian artery can be seen as stenosis or occlusion, and the stenosis can be seen as flow disturbance and increased flow velocity, while the artery distal to the stenosis becomes a low resistance change; the vertebral artery flow reversal, and the beam arm test can increase the positive detection rate. 3.T-angiography (CTA) or magnetic resonance angiography (MRA): it is the preferred method, which shows atherosclerotic plaque in the wall of the subclavian artery proximal to the beginning of the vertebral artery, narrowing or occlusion of the lumen, and provides a comprehensive understanding of the morphology of the aortic arch and its major branch arteries. 4.Digital subtraction angiography (DSA): It is the gold standard for diagnosis. It can be seen that the proximal subclavian artery at the beginning of the vertebral artery is narrowed or occluded, and the contrast of the affected vertebral artery is reduced, and even the contrast agent can be seen to flow backwards through the contralateral vertebral artery to the affected vertebral artery and reach the distal end of the subclavian artery.