The influence of the low voltage pulsed magnetic field (LVPMF) on the microstructure transition of K4169 superalloy was investigated. The gradient microstructure of K4169 superalloy composed of columnar grains, coarse grains, and fine grains was prepared through the combined method of LVPMF with directional solidification, which provided a new approach for the preparation of superalloy with gradient microstructure. The distribution of the Lorentz force and flow field under LVPMF effect was simulated, and therefore the microstructure transition mechanism was revealed. Results show that the microstructure transition should be attributed to the coupling effects of the Lorentz force and forced convection.