This paper focuses on predicting the contact fatigue life of the mooring buoy clasp joint structure by using the finite element program ANSYS/Fatigue. Mises equivalent stress is choosed as a stress-related fatigue criterion. An evaluation method of fatigue life under the pressure of buoyancy and wave force is established for the mooring buoy clasp joint structure. Firstly, wave force is treated as Morison dynamic force here and mooring buoys vibration model is conducted to analyze the dynamic response characteristics of vertical vibration of the mooring buoy. Secondly, dynamic contact stress calculations are conducted by directly exerting calculated vibration loads on the mooring buoy, and the stress spectrums of nodes are obtained. Finally, the S-N material fatigue curve and the Miner linear cumulative damnification principle are commonly applied to evaluate the contact fatigue life of the mooring buoy. The results show that the finite element program ANSYS/Fatigue can solve the contact fatigue problem simply, economically and efficiently. It also provides an effective engineering analysis method for these kinds of fatigue problems of the underwater mooring buoy.