Abstract: In this paper,based on the theory of damage mechanics, using damage equivalent stress to calculate the damage under 3 D stress status and taking the close effect into account,a subroutine to calculate damage and predict fatigue life on ANSYS platform was developed by APDL and UPFs of ANSYS.The initiation and growth of cracks are simulated by damage developing.The effect of damage on material properties has been taken into considerations by two ways,one is the method of stiffness matrix modification,the other is the effective stress method.The comparison between fatigue test and calculation results indicates that this method is right and feasible,and high accuracy can be obtained when there are no initial defects in PM components.Concerning components with initial defects,a method to simplify the initial defects by means of initial damage was put forward,and was used to evaluate the life of a specimen with initial defects.The method developed in this paper can be used to predict the life of PM components accurately as long as its initial damage has been obtained in relation to its initial status exactly.If the distribution probability of initial damage is known,the reliability design and evaluation of PM components can be carried out by this method.