The work aims to develop plasma boron-nitriding (PNB) technology to further improve the hardness of 42CrMo4 steel nitriding layer and comparatively study the properties of plasma nitriding layer. Under the same technological conditions of 520 ℃ and 6 h, 42CrMo4 steel was treated by plasma boron-nitriding and plasma nitriding, respectively. The cross-sectional microstructures, phase compositions, cross-sectional hardness, wear and corrosion resistance of the nitriding layer was tested and analyzed by optical microscope, XRD, microhardness tester and wear tester and electrochemical workstation. PNB significantly increased the nitriding efficiency. Under the technological conditions of 520 ℃ and 6 h, the thickness of compound layer and effective hardening layer increased from 18.78 μm to 29.44 μm, and 265 μm to 355 μm, respectively. Meanwhile, FeB and Fe2B were formed in the surface layer after plasma boron-nitriding, which significantly improved the hardness and wear resistance of nitriding layer. The surface hardness increased from 750HV0.05 to 1 002HV0.05, and both wear and corrosion resistance were obviously enhanced. The wear rate was decreased from 3.06 mg/cm2 to 1.02 mg/cm2, and the self-corrosion potential was increased from –648.89 mV to –494.32 mV. Compared with plasma nitriding, plasma boron- nitriding has obvious advantages, which can not only improve the efficiency of plasma nitriding, but also significantly improve the properties of the nitriding layer, including hardness, wear resistance and corrosion resistance.