Ultrasound diagnosis of carotid artery stenosis is relatively reliable, second only to angiography. The structure of carotid artery is divided into intima, mesima and epima, and lesions rarely occur in the epima, and lesions mainly occur in the intima and mesima. The thickness of the intima-media is <1mm under normal circumstances. If the thickness of the intima-media is between 1.0-1.4mm, the diagnosis is intima-media thickening, and if the thickness of the intima-media is >1.5mm, the diagnosis is plaque. If the plaque volume is relatively large, it can cause carotid stenosis. Originally, the degree of carotid stenosis was diagnosed by area, but now the Chinese Ultrasound Medical Branch has corrected it to four levels according to blood flow velocity. Level I is <50%, systolic blood flow velocity <125cm/s, diastolic blood flow velocity <40cm/s; Level II is >50%, <70%, but systolic blood flow velocity is >125cm/s, <230cm/s, diastolic blood flow velocity is >40cm/s, <100cm/s; grade III is >70%, <99%, systolic flow velocity is >230cm/s, diastolic flow velocity is >100cm/s; grade IV is lumen stenosis up to 99%, almost no blood flow signal, close to occlusion. If there is no complete occlusion or >70%, clinical intervention is required, either by stent placement or endothelial stripping, to improve the blood circulation in the carotid artery.