The difference between taking blood pressure lying down and sitting down is due to the difference in the amount of blood returned to the heart. Blood pressure is the pressure that acts on the walls of the blood vessels as the blood flows through them, and it is the driving force behind the flow of blood through the vessels. When blood pressure is measured lying down, the body is in the flat position, the amount of blood returning to the heart increases compared to sitting, the ejection of blood from the heart will increase, and the blood pressure value is high. In the sitting position, the return of blood to the heart is blocked, the volume of returned blood decreases compared to the sitting position, the ejection volume of the heart decreases, and the value of blood pressure decreases. However, whether lying or sitting, blood pressure measurement sphygmomanometer and heart at the same level, after sufficient rest, to avoid emotional excitement, the correct operation of the blood pressure value of the difference will not be very large, usually lying higher than sitting 5-10mmHg, if the difference is very large need to consult a doctor in a timely manner, to exclude related disorders. If the measurement of blood pressure is abnormal, it is recommended to consult a doctor in time to avoid delaying the condition.