Abstract: By taking the dual-scale strain energy density factor as controlling quantity, a multiscaling fatigue crack growth model is developed in this work. Hence, the whole fatigue failure process can be depicted in a consistent way by applying the proposed model. It no longer needs dividing a fatigue process into two different stages of fatigue crack initiation and propagation described by different approaches as usual. Then, the experimental S-N curves for different cyclic stress ratios are exactly re-produced by the proposed model. When the effects of material micro-structure are taken into account, the discrete fatigue test data can be re-produced. The results indicate that the size of initial micro-defects as well as the different evolution modes of material micro-structure have a pronounced influence on the fatigue life of specimens. The microscopic effect is a main reason of the scatter of fatigue test data.