Abstract: Given the technical features of the 18 acoustical circuit large diameter ultrasonic flow meters that are manufactured by Accusonic, an US company, and in order to measure water flow for unit 30 and unit 31 of Three Gorges underground hydropower station, a set of real time and effective flow measurement system was established. The system is able to conduct on-line efficiency calculation and analysis. This paper introduces the overall design scheme as well as technical implementation. The system can remotely control unit flow meter device and read the signal captured by the transducer of other unit flow meter through independently-designed locale control unit of switching box. At the same time, we can calculate the efficiency of hydraulic turbine, plot the efficiency curve and the scattergram of the distribution of pipeline flow regime by a human-machine interface, and etc. The system was used to test the efficiency of the units of Three Gorges underground power station, and the test results showed that its accuracy and the data fully met the standards.