The invention discloses a pressurized water reactor nuclear power unit primary and secondary loop system transmission power simulation method and system. The method comprises the following steps of: initializing the parameters of the pressurized water reactor nuclear power unit; obtaining the electric quantity data of the step size according to the preset rules; solving the primary loop system model and the secondary loop system model of PWR nuclear power unit and obtaining the calculation parameters. The final steam valve output power in the PWR nuclear power system model is calculated by using the calculation parameters, and the output power of the final steam valve is the transmission power of the primary and secondary loop systems of the PWR nuclear power unit. By fitting the specificenthalpy of the main steam and the feed water and taking into account the bypass discharge and the thermal efficiency of the unit, the method and the system solve the problem that the transfer power of the primary and secondary loop systems of the existing nuclear power unit model cannot be accurately calculated by adopting the method of calculating the enthalpy drop per unit time, and improve thesimulation accuracy of the nuclear power unit model.