<p>To investigate the influence of the local stress ratio on the fatigue performance of notched specimens, monotonic tensile tests, cyclic tension-compression tests, and fatigue tests on notched specimens were conducted on 2024-T4 aluminum alloy. The fracture surfaces of the fatigued notched specimens were examined using scanning electron microscopy (SEM) to analyze the microscopic fracture mechanisms, and the finite element method (FEM) was employed to analyze the stress-strain distribution around the notch. The experimental results indicate that the presence of a notch significantly degrades the fatigue performance of the material. Cracks consistently initiated at the notch root, and high stress levels promoted multiple crack initiation sites and the appearance of dimple features. The region where the stress ratio at the notch root varied coincided with the plastic deformation zone. The SWT model modified by the von Mises stress could predict the fatigue life in the low-cycle fatigue regime. The model incorporating the variation of the stress ratio at the notch root yielded satisfactory predictions for the fatigue life in the high-cycle fatigue regime. The stress ratio at the notch root was found to vary with the applied stress amplitude; therefore, the variation of the local stress ratio cannot be neglected when evaluating the fatigue life of notched specimens.</p>