The ankle-brachial index is obtained by measuring the systolic pressure of the ankle artery (posterior tibial or anterior tibial artery, taking the higher value) as well as the brachial artery, and obtaining the ratio between the systolic pressure of the ankle artery and the systolic pressure of the brachial artery.ABI is one of the most common and simplest tests used in vascular surgery. It is measured in a standard supine position. Usually, we use a sphygmomanometer that is specifically designed to measure blood pressure in the upper arm, and a special leg blood pressure cuff is used to measure ankle blood pressure to remove errors. Ankle blood pressure is mostly measured in the dorsalis pedis artery and the posterior tibial artery. The dorsalis pedis artery is located on the medial side of the dorsum of the foot and can be felt by normal people; the posterior tibial artery is located below the inner ankle and can also be felt by normal people, but it is not easy for non-professionals to find the exact location. Doctors generally use a Doppler stethoscope when measuring, which can capture the faintest arterial pulsations, and the measurement value is extremely accurate. The smaller the ABI, the worse the blood supply to the lower extremities. The range of the ankle-brachial index in a normal person at rest is 0.9-1.1, with 0.5-0.8 indicating mild or moderate ischemia in the arteries of the lower extremities and below 0.5 signaling severe ischemia. Patients with intermittent claudication tend to have an ankle-brachial index between 0.35 and 0.9, while patients with resting pain often have an ankle-brachial index below 0.4, and patients with resting pain have a higher likelihood of amputation. When the ankle-brachial index is greater than 1.3, it indicates severe vascular wall calcification. ABI has the advantages of being non-invasive, simple to operate, inexpensive, and easily accepted by patients. Therefore, the ankle-brachial index meter can be used both in clinical settings and for screening of large populations. The value of ABI in patients with coronary artery disease has been gaining attention in recent years. Reduced ABI has been found to be an independent risk factor for cardiovascular events and a strong predictor of total and cardiovascular mortality, with a 3-6 fold increase in coronary mortality in patients with reduced ABI. The rate of ABI positivity in diabetic patients was 25.9%, and the compliance rate of lower extremity ultrasound in positive patients was 100%, and lower extremity arterial disease in diabetic patients was positively correlated with medical history. The results of surveys in the United States, Europe, and Japan showed that smoking increased the incidence of lower ABI by 2 to 3 times. The prevalence of lower extremity peripheral artery disease among patients at high risk for coronary heart disease and ischemic stroke in China is 34.3%, and only 6.3% of patients with lower extremity arterial disease are diagnosed. Therefore, China is still faced with high incidence of lower extremity arterial disease, high disability rate, high mortality rate, low awareness rate, and low diagnosis rate. The situation of “three highs” and “three lows” with low treatment rate is severe. However, there are some limitations of ABI, such as the presence of severe middle artery calcification, stenosis or occlusion of the distal abdominal aorta or common iliac artery, and subclavian artery stenosis and occlusion, which may result in abnormal ABI values. In these cases, ABI cannot be used as a basis for diagnosis.