A new continuous measurement system of blood pressure using A-type ultrasonic wave ranging method is designed. The system uses ultrasonic wave sensor to detect carotid artery

obtain carotid artery diameter waveform by recognizing the reflected ultrasonic wave from front and back walls of the carotid artery to measure distance. Then establish blood pressure calculation model based on relationship between artery diameter and blood pressure

so as to measure blood pressure. Experimental results show that compared with the standard blood pressure measurement method

the maximum standard deviation of systolic blood pressure is 4. 72 mm Hg

the maximum standard deviation of diastolic blood pressure is 3. 17 mm Hg

which coincides with the standard of not more than 8 mm Hg made by AAMI.