<p>This study investigates the fatigue crack initiation behavior in gradient nanostructured (GNS) 316L stainless steel through fully reversed strain-controlled tension-compression fatigue experiments. The results reveal a pronounced dependence of crack initiation behavior on the applied strain amplitude. At strain amplitudes above 0.5%, crack initiation is primarily governed by surface features such as protrusions and rough regions. In contrast, at strain amplitudes below 0.5%, the dominant mechanism transitions to internal inclusions. Based on the proposed finite element and fatigue life model, we elucidated the competition between driving forces and resisting forces within different structural units, which ultimately govern the fatigue crack initiation sites. Furthermore, our results highlight the critical role of gradient nanostructures in the strain-sensitive crack initiation behaviors compared to residual stress. This study not only clarifies the competing fatigue crack initiation behaviors in GNS 316L stainless steel but also establishes a robust theoretical framework for analyzing crack initiation in other gradient structural materials.</p>