Abstract: The application of a pulsed magnetic field during the solidification process can refine the grains of the microstructure of material. In this study, the pulsed magnetic fields are applied in the pure liquid phase stage, liquid-solid two-phase stage, and the entire solidification process of Al-5%Cu alloy, to investigate in which stage the pulsed magnetic field functions and the influences of the process parameters of the pulsed magnetic field on grain refinement of alloy. It is found out that significant grain refinement effects are achieved when the pulsed magnetic fields are applied in the liquid-solid two-phase stage and the entire solidification process, indicating that the pulsed magnetic fields mainly act on the solidification nucleation process of materials. Besides, as the excitation voltage and magnetic field frequency increase, the grain refinement effect first increases and then remains unchanged. The optimized pulse electromagnetic parameters are that the frequency 5.0-10.0 Hz and the voltage 100 V.