In response to the phenomenon of delayed valve core reset failure caused by the viscous characteristics of lubricating oil in a certain type of solenoid valve in the field of nuclear power,a combination of finite element simulation and experiment was used to study the fault mechanism.A finite element model of the solenoid valve without oil film was established,and the normal valve core reset time was simulated.It is found that the friction coefficient has no effect on the valve core reset time.Through valve core reset time test and oil film viscous force test,the reset delay time of the sample and the mechanical characteristics of the piston oil film and the O-ring oil film were obtained.The results show that the viscous force of piston oil film and O-ring oil film is the main cause of delayed valve resetting failure,and the viscous force of piston oil film is the main cause.By simulating the piston oil film with bilinear constitutive equation using Cohesive element,simulating the viscous force of O-ring oil film using exponentially decaying concentrated force,the models of piston oil film and O-ring oil film were established,respectively.The finite element simulation of the valve core reset process under viscous force was conducted.It is found that the error in the reset delay time obtained from the simulation is relatively small compared to the experimental results,which proves that this simulation method can effectively simulate the delayed reset process of the solenoid valve core.