The 20mmHg difference in blood pressure between the left and right arms may be due to physiological reasons such as the different origins of the brachial artery in the left and right arms, as well as pathologic reasons such as vascular disease. 1. Physiological reasons: the different origins of the brachial arteries of the right and left arms may lead to a difference of 10mmHg-20mmHg between the blood pressure of the right and left arms. The right cephalic trunk artery supplies the right brachial artery, and the left subclavian artery supplies the left brachial artery, so the blood pressure of the right arm will be slightly higher than that of the left arm. 2. Pathological causes: vascular diseases such as subclavian artery or aorta may also lead to a 20mmHg difference in blood pressure between the right and left arms, such as arterial developmental abnormality, aortic narrowing, arterial entrapment, arteritis and so on. If the blood pressure difference of 20mmHg between the right and left arms has not improved or has a tendency to increase, or accompanied by other symptoms, it is recommended to go to the hospital in a timely manner to consult a doctor to determine the cause of the disease and then give targeted treatment according to the doctor’s instructions or treatment.