Aiming at the fault of a helicopter tail rotor blade fracture, the fault cause analysis is carried out by fault tree analysis method, and the bottom event analysis results are obtained. By carrying out failure analysis of the blade, the results of macro and micro fractographic analysis shows that the fracture property of the blade is low-stress and high-cycle bidirectional bending fatigue fracture. The simulation analysis of the fractographic damage evolution of flexible beam shows that when the strength value of the fiber compression direction of the flexible beam is less than 700MPa, the fractographic type is similar to that of the faulty tail rotor flexible beam. Comprehensive analysis shows that the tail rotor will produce large vibration under large fatigue load condition, and the increase of vibration intensifies the load of the tail rotor, leading to the increase of load at the root of the flexible beam, exceeding the designed bearing capacity of the flexible beam, then fatigue fracture at the root of the flexible beam of the blade.