Ultrasonic water meter uses the time difference method to measure the flow rate. An ultrasonic transducer is installed on the left and right of the measurement channel (pipe section), and transducer A transmits an ultrasonic signal to transducer B(forward flow), and transducer B transmits an ultrasonic signal to transducer A(reverse flow), in the transmission process, the positive flow and the reverse flow ultrasonic signal form a certain time difference. By measuring the time difference, the speed of the water flow can be calculated. When the cross-sectional area of the calibrated pipe diameter is used, the flow velocity is converted into the flow rate to realize the flow measurement.