In view of the impact of spalling failure on meshing stiffness and dynamic characteristics in planetary gear systems,energy methods were applied to analyze the time-varying meshing stiffness of healthy and the spalled gears.As the spalling length increases,the stiffness decreases significantly.According to the planetary gear system dynamics model,the vibration response of different spalling failure gears was simulated.The results show that spalling failure induces periodic impacts,the amplitude increases as the spalling degree grows;in the spectrum,fault frequency,its multiple frequency and side frequency components become more pronounced.An improved time-varying filtered EEMD method was introduced,effectively identifying failure characteristic frequencies.By comparing experimental signals with simulation signals,the effectiveness of the dynamics model and diagnostic method is validated.