There is a diurnal rhythm of blood pressure fluctuation in normal people, usually the blood pressure is lowest at 2~3 a.m., has a peak at 6~10 a.m. and 4~8 p.m., and begins to decline slowly after 8 p.m. This rhythm is more obvious in the elderly and hypertensive patients. This rhythm is more pronounced in the elderly and hypertensive patients, according to this law, clinical blood pressure measurement is usually chosen at the time of peak blood pressure, which has a certain role in guiding the treatment program for hypertensive patients. In hypertensive patients with a longer duration of illness, this daily rhythm of blood pressure may not be obvious or disappear, and it is considered that it may be due to vascular smooth muscle proliferation caused by long-term hypertension. In addition, the fluctuation of blood pressure is affected by many factors, such as changes in body position, emotional fluctuations, and strenuous activities, which may lead to errors. Therefore, it is recommended that patients should measure their blood pressure at a fixed time of the day, remain emotionally stable, and take measurements in a resting state in order to avoid errors.