Abstract: Nitridized steel parts have been widely applied in many fields, but the effect of the surface N content on the tribology of the nitridized parts and its mechanism has not been clearly understood. The surface N content of the N⁺-implanted 316L stainless steel samples was controlled by changing the dose, and the influence of the dose on the tribological performance of the N⁺-implanted samples under lubrication conditions and its mechanism were studied. It is found that with the increase of the dose from 0 to 2×10¹⁷ N⁺/cm², the friction coefficients, wear rates of both the implanted samples and their counterpart balls decreased, and the improvement of the tribological performance by N ion implantation under zinc dialkyl dithiophosphates lubrication conditions was more obvious. The mechanism was that a higher N content in the implanted layers promoted the formation of the polyphosphate with a shorter chain length and a higher hardness from zinc dialkyl dithiophosphates. However, the influence of the dose on the tribological performance of the implanted samples became unobvious when the dose was further increased to above 2×10¹⁷ N⁺/cm².