Aiming at the short operating time of the magnetic recoil physical power supply, the shock test and theoretical calculations are difficult to clarify its working performance, numerical simulation is carried out to analyse the power generation process for the magnetic recoil physical power supply. Taking the magnetic recoil physical power supply on a certain type of small-caliber ammunition fuze as an object. Based on the internal ballistics calculation results, the finite element analysis of the magnetic core motion and the induced voltage of the coil are carried out by LS-DYNA and Maxwell software, and the numerical simulation result accuracy has been verified by experiment. The total travel time of the core is 440μs and 875μs, and the output voltage of the power supply is 14.6V and 17.1V, under the sinusoidal and internal ballistic fitting loads. The result indicates that the accuracy of the simulation results is higher when the results of internal ballistic calculations are used as the parameter basis for the coupled simulation analysis of the physical power supply core motion and output voltage.