Abstract: Failure analysis was performed on the wing-fuselage joint fatigue specimens of an aircraft through macro/micro observation, microstructure examination, FEM analysis and fatigue tests. The results show that it is the higher load frequency, the asynchrony of the loads actuated by left and right cylinders and the insufficient constraints of web plate, that cause greater stress at the connecting bolt of the web, leading to the initiation of fatigue crack and the short fatigue life of the experimental samples. The amplification of fracture surface shows a large number of small fatigue curves and the fast crack propagation region shows the mixture feature of fatigue and dimples. Thus, the fracture failure mode is assumed to be the typical fatigue fracture. Finally, some improvement measures were put forward.