Abstract: In Daya Bay nuclear power plant,there have been many times that the module used to value the water level outputs a small pulse interference when the pressurizer water level control system is in operation,and the interference exists only in analog storage operation module,which can directly impact the control of the water level of the pressurizer,causing the water level fluctuations and adversely affecting the safe operation of the reactor.This paper analyzes the module incidental interference faults of the water level control system of the NPP pressurizer from the point view of the system control and design of module hardware,and finds out the reasons by the system simulation experiment and power supply circuit test.It is suggested to further improve on the design of hardware loops,add more inductance and capacity to eliminate the interference.