Abstract: To calculate the bending fatigue life of gears, the fatigue process was divided into crack initiation and crack propagation periods. The real working condition of gears was imitated with ADAMS software and a loading spectrum during the work process was gained. According to the loading spectrum the maximum stress in the dangerous cross-section of the gear root was analyzed by the finite element method based on ANSYS software. Fracture mechanics, the rain flow counting method, and the Miner fatigue cumulative damage model were used to predict the bending fatigue life of gears under the dynamic load, and two calculation models of bending fatigue life were proposed for crack initiation and crack propagation, respectively. To verify the calculation models, bending fatigue testing was performed on a high- frequency fatigue testing machine. The experimental data comply with the numerical simulation results, indicating the correctness of the theoretical analysis.