The work aims to study the micro-structure of different composite coatings and the effects on mechanical properties. Plasma nitriding, (Cr,Ti)N coating, nitriding+(Cr,Ti)N coating and nitriding+Cr+(Cr,Ti)N coating were strengthened on the surface of austenitic stainless steel by plasma enhanced magnetron sputtering system. The effects of different modified layers on micro-structure and mechanical properties were studied respectively by XRD, SEM, nano-indentation tester, pin-on-disk tribometer and scratch tester. After nitriding, supersaturated solid solution phase with high nitrogen content (γN) was formed with a few precipitations of Cr2N and Fe2N. The hardness and modulus were respectively 18.3 GPa and 264.7 GPa. The in-situ deposition of the coating after nitriding effectively prevented the precipitation of the nitride phase, and promoted the diffusion of supersaturated nitrogen into the substrate, thus increasing the depth of nitrided layer. The nano-hardness and modulus of (Cr,Ti)N coatings combined with nitriding were higher than those of single (Cr,Ti)N coating (20.2 GPa and 271.8 GPa), and those of ni-triding+(Cr,Ti)N were the highest (25.4 GPa and 345.6 GPa), followed by those of nitriding+Cr+(Cr,Ti)N (22.4 GPa and 326.3 GPa). The adhesion strength of (Cr,Ti)N coating combined with nitriding was the highest due to the gradient transition of nitrided layer, which improved from that of the single coating of 9.5 N to 53 N. The friction coefficient decreased to 0.43, and the wear-rate was the minimum, namely 0.66% of that of the substrate. The (Cr,Ti)N composite coating combined with nitriding has the best mechanical properties.