In the present study, the composition of ion nitriding layer of forged CoCrMo alloy was analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The tribocorrosion was investigated in 25% calf serum solution. The results showed that CrN and Cr2N phases formed in ion nitriding layer. The content of CrN phase was about 70.2% and Cr2N is only about 29.8%. The corrosion potential (Ecorr) of ion nitriding sample was about −310 mV and the untreated sample was about −820 mV. On condition of tribocorrosion, the friction coefficient of untreated sample was less than those of nitriding sample under different applied loads. At the same applied load, the current density of ion nitriding sample was higher than that of the untreated one. Ktot and Kw of ion nitriding sample were less than the untreated one, which showed the better tribocorrosion resistance. The ratio of Kc/Kw for ion nitriding sample lied in the range of 0.1 < Kc/Kw < 1 under three tested loads, showing that the mechanism was controlled by a wear dominated corrosion.