Abstract: Two-stage vacuum nitriding process was used to modify the surface of quenched and tempered PCrNi3Mo steel. Under the condition of the same nitriding temperature and nitrogen potential, the microstructure, phase composition, hardness and wear resistance of the surface layer of the test steel were studied under the conditions of strong infiltration for 6 h and diffusion for 6 h, and compared with those by strong infiltration for 4 h and diffusion for 8 h. The results show that after nitriding, the phase of the test steel surface layer was ε-Fe_2-3N phase. Under two nitriding time conditions, the thickness of nitrided layer was about 0.6, 0.7 mm, and the surface hardness was 660.3, 581.3 HV, respectively, higher than 360 HV of substrate. Under the former nitriding time condition, the compound layer in the nitriding layer had poor compactness and a great number of micropores; the hardness transition of the nitriding layer was good, and the hardness was relatively high at the distance from the surface of greater than 0.3 mm; the friction coefficient and wear amount of the nitrided layer were relatively low, and the furrow on the wear surface was shallow, indicating the wear resistance was relatively good.