Abstract: Operation efficiency is a key design parameter of hydro turbine units, but it cannot be directly measured and has to be calculated through the measurement of flow rate and other related parameters. Therefore, precise measurement of flow rate is crucial to improvement on its calculation accuracy. In this work, we have developed an efficiency tester of hydro turbine units working in various loading conditions, using the current meter method and a LabWindows CVI platform. The testing is consistent with the related test procedure and can meet the practical needs of turbine unit tests. Application of the tester in power plants validated its feasibility and accuracy. The results indicate that the measurements of flow rate agree well with its real values, and that this new tester can save a large amount of calculation and thus is worth wide application.