Abstract: A micromagnetic method was used to investigate the effect of grain boundary phase structure, grain size of the main phase, and main phase composition on the magnetic properties of multi-main-phase (Nd, Ce)-Fe-B magnets.The results demonstrate that when the grain boundary phase is nonmagnetic, the grain boundary phase along the grain boundary is thicker, which is more favorable to the improvement of the coercivity H_cj.With the magnetism of grain boundary phase increasing, the coercivity H_cj of the magnet reduces dramatically. Meanwhile, the refinement of main phase grain helps enhance the magnet coercivity H_cj.As the grain size decreases, the coercivity H_cj of the magnet gradually increases.Moreover, after diffusion of Pr and Dy, a hard magnetic shell layer of ((Nd, Ce)_1-xRE_x)₂Fe₁₄B (RE=Pr/Dy)is formed on the surface of the main phase grains, resulting in an increased nucleation field and thus a significant improvement in the coercivity H_cj.