Abstract: The surface of H13 steel was boronized, and the effect of the content of rare earth CeO₂ (0, 2wt%, 4wt%, 6wt%), boronizing temperature (850, 900, 950, 1 000 ℃) and boronizing time (2, 3, 4, 5 h) on the microstructure and properties of the boronized layer were studied. The results show that the thickness of the boronized layer increased first and then tended to be stable with increasing boronizing temperature and time. When the content of CeO₂ increased from 0 to 2wt%, the diffusion activation energy of boron atoms did not change much, and decreased obviously from 2wt% to 4wt%, and the thickness of the boronized layer increased faster. The content of CeO₂ increased from 4wt% to 6wt%, the diffusion activation energy basically unchanged, the thickness of the boronized layer increased slower. The boronized layer with 4wt% CeO₂ formed at 950 ℃ for 4 h had the least holes, the most dense microstructure, the highest hardness, and the best wear resistance.