In this paper, a stress gradient correction method for full-stage life prediction models is proposed on the basis of the existing studies. Different from the existing methods, the new method does not need the local dimensions of the structure but determines the critical distance according to the stress gradient curve, which avoids the distortion due to the excessive variation of the local dimensions of the structure and improves the applicability. Smooth and notched test specimens were designed to complete the processes of modelling, fitting parameters, and life prediction, which verified the validity and fitting accuracy of the new method. The study incorporated fatigue test specimens containing two distinct notches, which are designed to ensure equivalent stress and strain levels at the notch root through dimensional engineering, to underscore the pivotal role of stress gradient in fatigue life prediction. Furthermore, the novel method was applied to fatigue life prediction of aero-engine compressor disc and validation experiment was completed. The results demonstrate that the stress gradient correction method proposed in this paper exhibits high accuracy in predicting both the life and the damage location, and more accurately reflects the degree of stress concentration at the dangerous location of the actual structure.