Abstract: The fatigue crack growth behavior of 5 mm thick 7050 aluminum alloy friction stir welding joints in different areas was analyzed and studied. The results show that the fatigue crack growth rate is the fastest in the weld nugget zone. The second is the position of the thermo-mechanically affected zone of advancing side. The fatigue crack growth rate is the slowest in the thermo-mechanically affected zone of retreating side. The fatigue crack is propagated by intergranular and transgranular mixing in the weld nugget zone, while the crack is propagated by transgranular in the thermo-mechanically affected zone. The deflection of the crack and the generation of the crack branch will reduce the fatigue crack growth rate. In the initial stage of fatigue crack growth, the fracture surface of the weld nugget zone is distributed with grain size fracture planes, and fatigue striations are generated; fatigue striations did not occur in the thermo-mechanically affected zone, but tire indentation patterns appear here. During the steady-state propagation of fatigue crack, the crack growth rate increased, and fatigue striations appeared in the weld nugget zone and the thermo-mechanically affected zone, and secondary cracks were generated.