The surfur-nitrided layer on the surface of LZ50 steel was prepared by surfur-nitrided duplex processes.The rotational fretting wear tests of diffusion layer and substrate were carried out under different angular displacement amplitudes in dry condition.The wear scars were analyzed by optical microscope,scanning electric microscope,energy dispersive spectroscopy(EDX)and 2D/3D profilometer.The experimental results show that the surfur-nitrided layer changes the running condition fretting map of the substrate.The boundary between partial slip regime and slip regime moves to the partial slip regime,and the width of the slip regime is broadened.In the partial slip regime,the friction coefficient of the diffusion layer is significantly lower than that of substrate，and the damage of the diffusion layer is very slight.In the slip regime,the friction coefficient of the diffusion layer is higher than that of substrate due to hard particles peeling from subsurface in steady stage,and the wear mechanism of the diffusion layer is mainly abrasive wear,oxidative wear and delamination.