Aiming at the crack problem, a translationtorsion coupling dynamics model of singlestage planetary gears was established by the lumped centralized method, considering timevarying meshing stiffness, support stiffness, integrated meshing error and meshing damping. The response characteristics of a single planetary gear under different crack degrees were analyzed, and the response characteristics of the system under different planetary gear failures were analyzed. The results show that, when a single planetary gear has a crack failure, the double frequency is the main energy. As the degree of crack increases, the vibration of the system becomes severe, and the proportion of the energy of the double spectrum increases gradually, the phase diagram gradually changes from the inner character to the singlecircle curve, and the system motion tends to be stable. When the number of planetary gear failures increases, the vibration severity of the system becomes smaller than that of a single faulty planetary gear, and the spectral energy distribution changes more obviously. The proportion of the double frequency energy is getting smaller and smaller and the internal curve is gradually separated from the external curve. The research in this paper has certain theoretical significance for the crack fault diagnosis of singlestage planetary gearbox.