To improve the nuclear safety, the shaftless canned motor is applied to the reactor coolant system of the new ressurized water reactor . Because of the different between the gernal shaft sealing pump and the the shaftless canned pump , the shaftless canned pump has a less rotary inertia with different dynamic response characters.The main pump is sensitive to voltage and frequency fluctuation and has a less rotarty intertia . Based on these characteristics , a dynamic model with friction torque taken into account of shielded main pump is established and it has been connected to the simulation model nuclear power unit system.The effectiveness of the main pump dynamic model and the frequency and voltage disturbance response characteristics of the main pump is been simulated and verified. Besides, the influence on the core power is analyzed. The results show that the friction torque has a significant effect on the half-flow idling time of the main pump, and this characteristics should be taken into account. The influence of the frequency disturbance on the main pump speed and flow is more obvious than the voltage disturbance. Power supply quality should be improved in operation