Abstract: According to the different fatigue damage cumulative quantity, the dynamic response frequency is measured during the fatigue damage process. The results of experimental study show that the natural frequency varies nonlinearly with the fatigue damage fraction. A new fatigue damage parameter is proposed, which is described by the nonlinear relationship between the natural frequency of specimen and its cyclic ratio. On the basis of continuum fatigue damage theory, a nonlinear fatigue damage evolution model is developed. The results show that the proposed fatigue damage parameter can describe well the characteristics of fatigue damage. The predicted errors of fatigue life are within two factors.