Subclavian artery steal syndrome is a syndrome in which there is partial or complete occlusive damage in the subclavian artery or the proximal segment of the vertebral artery at the beginning of the cephalic trunk, causing retrograde flow in the affected vertebral artery into the distal end of the affected subclavian artery due to siphoning, resulting in ischemic episodes in the vertebrobasilar artery and ischemia in the affected upper extremity. There can be symptoms of cerebral ischemia or upper extremity ischemia. 1.Transcranial Doppler ultrasound (TCD) detects the blood vessels and blood flow in the neck, and the reverse flow signal of the vertebral artery can be seen, and a bundle arm test should be performed on the affected side if suspected. 2, color Doppler ultrasound can be seen at the beginning of the subclavian artery stenosis or occlusion, the stenosis can be seen in the blood flow disorder, increased flow velocity, the distal artery of the stenosis becomes low resistance changes; vertebral artery blood flow reversal, the beam arm test can increase the positive detection rate. CT angiography (CTA) or magnetic resonance angiography (MRA) is currently the preferred method, which can show atherosclerotic plaque in the wall of the subclavian artery proximal to the beginning of the vertebral artery, narrowing or occlusion of the lumen, and provide a comprehensive understanding of the morphology of the aortic arch and its major branch arteries. 4.Digital subtraction angiography (DSA) is the gold standard for diagnosis. It can be seen that the subclavian artery is narrowed or occluded at the proximal end of the vertebral artery 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.