<p>The fatigue crack growth behavior of Al 6061-T6 alloy with inclined cracks is studied through theoretical derivation, numerical simulation, and experimental verification. A modified fatigue crack growth model taking into account of crack closure effect under mixed-mode I and II loading condition based on Paris equation is analyzed theoretically. Initial cracks with different inclination angles (β = 0°, 30°, and 60°) are prefabricated on Al 6061-T6 alloy plates with the thickness of 10&#xa0;mm. The fatigue crack propagation process of the alloy is investigated by experiment and finite element simulation. The results indicate that the crack propagation path of the specimen with inclined cracks is generally consistent with the direction perpendicular to the cyclic loading during the crack growth process. Crack propagation mainly includes two stages: initial propagation and stable propagation. The initial crack propagation is closely related to the inclination angle β. The larger the angle β is set, the slower the initial crack propagation rate becomes. During the stable propagation stage, the crack has completely transformed from a mixed mode I and II to a pure mode I. The propagation rate of the entire crack front is consistent, and the shape of the crack front is also similar.</p>