Abstract: Cracking occurred to the elastic pieces of tail nuzzles in aero engines for several times. The failure mode and cause were analyzed by visual inspection, fracture analysis, energy spectrum analysis, metallographic examination, flow field analysis and stress analysis. Results indicate that the cracks are multi-source fatigue cracks, initiating from the weld joints between the sheets of the elastic pieces. The larger aerodynamic load caused by abnormal flow field were the main reason for the fatigue cracking. Meanwhile, the safety margin of the 0.5 mm TC2 sheets is insufficient and there are incomplete fusion defects at the weld joints, resulting in stress concentration and reducing fatigue resistance. The two factors promoted the initiation of the fatigue cracks. Finally, some improvement measures were put forward to avoid similar failure.