Abstract: Fatigue damage of metal component is a kind of mechanical damage, so the main external cause of fatigue damage is stress amplitude and the internal one is intrinsic property of material. Based on the general damage evolution equation of damage mechanics and Paris formula of fracture mechanics, a new model of fatigue damage evolution is proposed by using the dominating variables of the effective equivalent stress amplitude and the characteristic parameters of damaged material. As an example, an experiment on 12Cr1MoV steel is carried out. It is shown that the new model is simple, and in better agreement with the experimental result than Lemaitre model of damage mechanics.