The work aims to study the evolution of nitriding layer structures and tribological properties with time under different discharge current densities and the diffusion and precipitation mechanism of nitrogen in stainless steel. The surface of austenitic stainless steel was modified by hot wire enhanced plasma assisted nitriding. The phase composition and structure of nitriding layer were studied by XRD and XPS, the cross-section morphology of nitriding layer was observed by SEM, and the nitrogen content and distribution with depth were analyzed by energy spectrum. The tribological properties of nitriding layer were studied by nano-indentation, wear tester and step tester, respectively. When the current density was 0.81 mA/cm2, a single supersaturated solid solution phase was formed on the surface of stainless steel after nitriding for a short time (1~2 h). As nitriding time increased to 4 h, the phase was converted to more stable Fe4N phases, the thickness of nitriding layer reached 14.2 μm, and the surface hardness reached 17.81 GPa. When the current density increased to 1.25 mA/cm2, the binding energy between N and metal atoms increased, and the CrN and Fe4N phases began to precipitate after nitriding for 1 h. After 4 h, the surface hardness and modulus increased to 22.88 GPa and 314.2 GPa, respectively, and the wear rate was only 0.6% of that of the substrate. The diffusion coefficient of N atom in austenite increases in direct proportion to current density. With the increase of nitriding time (or hot-wire current), the thickness of nitriding layer and Vickers hardness increase obviously. The increasing trend is proportional to one-half power of time. The single solid solution phase γN of nitriding layer is transformed into solid solution phase CrN and Fe4N with a small amount of nitride precipitates. The tribological properties of nitriding layer are improved obviously.