The work aims to explore the relationship between the phases of compound layer and wear resistance, and realize its effective regulation, so as to meet the service performance requirements of different parts. The common nitriding steel 38CrMoAl was selected for plasma nitriding with different nitrogen ratios (15%, 20%, and 25%) at the nitriding temperature of 510 ℃ for 4 hours. The microstructure, phase constituents, cross-sectional microhardness and wear resistance of the nitriding layer were tested and analyzed by optical microscopy (OM), X-ray diffraction (XRD), microhardness tester and friction and wear tester. At the same nitriding temperature, the compound layers with different phase composition could be obtained by adjusting nitrogen ratios. When the nitriding temperature was 510 ℃ and the nitrogen ratio was 20%, the critical nitrogen potential for the formation of the γ‘ phase was satisfied, thus the γ‘ single phase compound layer was obtained. When the nitrogen ratio reached 25%, the critical nitrogen potential for the formation of the ε phase was satisfied. The dynamic formation and transformation of the γ‘ phase in the nitriding layer into the ε phase increased the ε phase gradually and ε+γ‘ biphasic compound layer was obtained. The ε+γ‘ biphasic compound layer formed by 38CrMoAl after plasma nitriding with different nitrogen ratios has better wear resistance at a small wear load of 200 g. However, when the wear load is 400 g, the wear scar and the friction coefficient of γ‘ single phase compound layer are narrower and smaller at 20% nitrogen ratio. That is to say, under the heavier wear load, the wear resistance of the γ‘ single-phase compound layer is better than that of the ε+γ‘ biphasic compound layer. This study can provide reference for the design of ion nitriding process for parts with different wear and service conditions.