Effects of added cerium oxide rare earth in the boronizing agent on the structure and thickness of boronizing layer for Q345 steel were studied, and the rare earth catalysis process by using the orthogonal testing method was determined. The analysis shows that adding appropriate amount of cerium oxider are earth can significantly improve the boronizing layer structure and increase the thickness of more than 10%. Orthogonal testing results show that the best rare earth catalysis process can be gotten when the temperature is 920 ℃ and the time is 7h and the oxide rare is 2%.