It is necessary to measure the circulating water flow in hydropower station. Since the pipe diameters that need to be measured belong to large models, namely DN6000 models and DN3000 models, after comprehensive analysis and demonstration of the flow to be measured and various types of flowmeters, it is finally believed that the more economical, applicable and feasible ultrasonic flowmeter can be used to solve the problem. Therefore, the ultrasonic flowmeter was selected to measure the circulating water flow accurately, and the corresponding problem was solved.