Abstract: Cr Al N coating was prepared on 50 BA steel after nitriding by multi-arc ion plating. Then, the mechanical and friction properties of substrate, nitriding layer and coating were tested by microhardness tester and friction and wear tester.Finally, the surface morphology of the coating was characterized by scanning electron microscope（SEM） to observe the wear morphology of the sample and to analyze its wear mechanism. The results show that compared with nitriding layer and substrate, the hardness of the Cr Al N coating is the highest, which is 5.2 times higher than that of the substrate. The wear degree of the coating is obviously the lowest, 50 BA steel surface quality is obviously improved. The wear resistance has been greatly improved.