Abstract: The pulse plasma nitrocarburizing technologies of 42CrMo steel under different temperature and time conditions with and without RE addition were studied. With microstructure and XRD analysis indicated that the effect law to the plasma nitrocarburing of RE. The result showed that RE can improve the microstructure and decrease the compound layer depth of earlier nitriding ;RE can decrease ε and increase γ′. RE can increase the surface nitrogen concentration.