This paper describes an ultrasonic vortex flowmeter composed of an ultrasound transmitter,an ultrasound vortex sensor,an ultrasound receiver,a detector,an amplifier,Schmitt flip-flop,and a set of other devices for calibration. The output of meter is a frequency signal which changes with magnitude of air flow. The range of measurement is 30~1800 ml/s of gas or steam with a pressure loss of 1.0 kPa. The transient accuracy,average accuracy,and accuracy by power spectrum come up to 6.2%,4.4% and 0.5% respectively. It can be used in the measurement of the ventilation and monitoring of human breath.