A blood pressure detection method is used for the sphygmomanometer including an envelope, an air pressure control mechanism, an ultrasonic wave transmission mechanism and an ultrasonic wave reception mechanism. The blood pressure detection method includes: applying a control signal to the air pressure control mechanism and the ultrasonic wave transmission mechanism, to inflate and deflate the envelope, and enable the ultrasonic wave transmission mechanism to transmit an ultrasonic detection signal toward the to-be-detected body part at a predetermined interval； monitoring an ultrasonic reflection signal received by the ultrasonic wave reception mechanism； determining a detection time point for the blood pressure detection in accordance with a frequency of the ultrasonic reflection signal during the deflation of the envelope； and determining a blood pressure value for the blood pressure detection in accordance with a pressure value of air within the envelope at the detection time point.
