Based on the lumped parameter method,the dynamic model of the planetary gear with cracks in the sun gear was established.An improved meshing stiffness method considering the gear tooth transition curve was proposed,and the time-varying meshing stiffness calculation method under the gear health state and crack state was derived.On this basis,the vibration response was solved.The simulation results show that when the root crack occurs,the vibration response of the root has obvious impact response characteristics,and the characteristic frequency and frequency doubling characteristics of the sun gear fault can be obtained.Finally,by comparing the simulation signal with the test signal,the test results are in good agreement with the simulation results,which verifies the effectiveness of the proposed dynamic model.