Abstract: Based on the occurrence mechanisation of cavitation, this paper develops an online monitoring technology to determine the occurrence of cavitation in hydraulic turbine and judge the severity of cavitation by analyzing the change of time-frequency characteristics of cavitation noise radiated by hydraulic turbine during cavitation. This technology has been applied in many hydroelectric power stations including bulb turbine, Kaplan turbine, Francis turbine and pump-turbine. It has the characteristics of convenient installation, safety and reliability, and can be applied in the fields of optimal operation of hydraulic turbine and smart unit construction.