Abstract: The behaviour of mixed-mode fatigue crack propagation has been studied experimentally by using tension panels with oblique crack. The results obtained from the fatigue tests with precracked specimens and machined slit specimens are compared. An engineering method for calculating the stress intensity factors of the stiffened panels is proposed. The crack growth path and ax-N curve under combined-mode fatigue loading are predicted by the methods proposed by Sih and Wang Maohua. Comparisons between the predictions and test results show that the method proposed in this paper is satisfactory for engineering purpose.