al zone approach, the stress eigenvalues of a certain point, line or area in the vicinity of notch are used as the failure criteria. This paper presents a reasonable explanation for notch effect. The refore, critical zone approach is considered as a fatigue life predicton method for notched specimens with a promising prospect in engineering application. The stress field intensity approach and the theory of critical dis tances for three-dimensional structures are first elaborated considering three-dimensional engineering structure characteristics. Several parameters are accurately defi n ed and described. Then the two methods and the nominal stress approach are app lied to predicting fatigue life of an aero engine disc. The results indicate that t he proposed stress field intensity approach and the theory of critical distances for three-dimensional structures provide an excellent prediction on fatigue life. The two methods have a better prediction effect than the nominal stress approach.