The paper focus on the fatigue failure of welded joints affected by welding defects, fatigue and crack growth tests were conducted on 1Cr11Ni2W2MoV argon arc welded joints, which were used as certain engine’s combustion chamber case. Based on these tests, the NASGRO equation was established to describe the entire process of crack expansion in the welded joints. Then, the modified NASGRO model describing the whole process of crack expansion of the welded joints was established by considering the changes of threshold value and closure parameter in the expansion of the short cracks on the basis of the NASGRO model. Using modified model, the initial weld defects were equated to regular cracks, and the fatigue life of the welded joints under different stress levels was calculated by the crack growth method. Comparative analysis with the test results show that the model predictions are all within the twice dispersion band. The crack growth life prediction method developed in the paper provides certain guiding significance for the fatigue life study of welded joints considering the influence of defects.