There are many diseases that can cause a small pulse pressure difference, which can basically be divided into three parts: 1, the most common cause of a small pulse pressure difference can be seen in hypotension, pericardial effusion, constrictive pericarditis, severe aortic or mitral stenosis, etc., is the most common clinical situation, to confirm the diagnosis requires the improvement of cardiac ultrasound, ambulatory blood pressure monitoring and other tests. 2, renal hypertension, due to increased peripheral resistance caused by increased diastolic blood pressure The patient’s pulse pressure will also be small. It is necessary to test the kidney function and understand the medical history according to whether the patient is combined with kidney disease. 3, due to obesity, increased blood viscosity or combined with diabetes, hyperlipidemia, etc., can also cause a decrease in pulse pressure difference. This type of patient is more difficult to diagnose and other organic diseases need to be excluded to confirm the diagnosis.