Abstract: The fatigue test for 7050-T7451 high-strength aluminum alloy thick plate was carried out, and the fatigue fractures at different stress amplitudes were observed by optical microscopy and scanning electron microscopy. The microscopic characteristics of crack initiation region and crack propagation region of the alloy were analyzed with an emphasis. The results showed that the fatigue cracks initiated from or near the surface of the specimen where the brittle Fe-rich compound inclusion particles were. The distance from crack initiation to the surface was 158.64 μm under stress amplitude of 240 MPa, while it was 120.10 μm under the stress amplitude of 340 MPa. The micro characteristics of second crack and cliffs exhibited on crack propagation region. And the larger the stress was, the wider the fatigue striations were.