To forecast the fatigue life of spline couplings accurately, taking the interaction of fretting wear and fretting fatigue into account, the fretting damage mechanism of a spline coupling was investigated, the prediction methods of fretting fatigue were analyzed, and by ignoring the position and direction of fatigue occurring, a new damage accumulation method based on SWT method for spline was provided, and the fretting fatigue life of this spline coupling under the given conditions was predicted. The results show that in the fretting process of spline coupling fretting wear and fretting fatigue competes and restrains with each other and leads to the spline coupling fatigue failure under the effect of two fretting modes eventually, the fatigue life of the spline coupling decreases with the SWT increasing. The damage accumulation method can reflect the effect of fretting wear on the fretting fatigue accurately, it gives a numerical reference for the designing and repairing of spline coupling, and at the same time, it also provides a basis for the further study of prediction fretting fatigue life in spline couplings which have clearance between the teeth.