The experiment studies a method of measuring liquid velocity by Doppler effect in this text．This method is an ingenious combination of the principle of the measurement of ultrasonic waves by ultrasonic gratings and the Doppler effect．The liquid velocity can be measured by the frequency differential between the incident wave and the reflected wave generated by ultrasonic waves propagating in a constant fluid environment．It provides a new idea and method for the measurement of liquid velocity，which will enrich experimental teaching content and increase experimental innovation scheme，and which can be used for enlightening the innovative design thinking of experiment．