To enhance the tribological properties of an as-cast equiatomic NiCoCr medium-entropy alloy (MEA), surface modification was performed via nitrogen ion implantation. The influence mechanism of N-ion implantation on the wear resistance of NiCoCr MEAs was systematically investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results indicate that nitrogen ion implantation introduces the CrN phase into the NiCoCr MEA surface, significantly increasing its microhardness to 373.1 HV0.1 (1.69 times greater than that of the as-cast alloy). Compared with the as-cast state, the modified alloy demonstrates substantially superior wear resistance, with a reduced wear volume of 6.79×10-2 mm3 when sliding against a ZrO2 counterpart. The sliding frequency has a pronounced influence on the tribological behavior: the friction coefficient initially increases and then decreases with increasing frequency, whereas the wear rate has the opposite trend. In addition, wear mechanisms exhibit frequency dependence: at low frequencies (1 Hz), oxidative wear and adhesive wear dominate, accompanied by cracking and plastic deformation; at higher frequencies (2~5 Hz), abrasive wear prevails alongside oxidative wear and minor plastic deformation.