Abstract: The running current of EH oil pump motor operation for a 1000 MW steam turbine unit in some thermal power plant gradually increased.It increased by 3 A in 10 days, about 13% higher than the normal running current, and there was a trend to continue to increase.The internal leakage of the hydraulic electro-hydraulic servo valves of the main steam control valves of the two small turbines was analyzed by observing the movement of the valve stems of the main steam valves and the main steam control valves and measuring the temperature difference of the EH oil inlet and return pipes of the hydraulic servo motors.The internal leakage fault of the servo valve was further confirmed by closing the small turbine control valve.It analyzed the layout of EH oil system, determined the feasibility of online replacement of servo valve, and timely implemented it in the low load stage of the unit. After replacing the two small electromechanical servo valves, the running current of the EH oil pump motor returned to the normal value.