Disclosed is a method of predicting damage of dies for plastic processing of metals, typically, forging dies, to contribute to die design including choice of material, hardness and configuration of the die. The method is characterized in that the plastic flow criteria value “Dc” defined by the formula below is calculated: Dc=σeq/(YS×SRtotal), wherein σeq is Von Misese's equivalent stress, YS is dynamic compressive yield stress, and SRtotal is softening rate, and that the damage of die is predicted with the condition that, if the value of Dc reaches 1.0, the plastic deformation or the plastic flow begins to occur