Aimed at the influence of fault factors on the dynamic characteristics of planetary gear transmission system, the Hertz contact theory was used to establish a new dynamic model of transmission system by introducing bending stiffness under the condition of considering the contact stiffness characteristics of tooth surface. The change of torsion spring stiffness was used to introduce the two fault factors of solar wheel crack and broken teeth respectively; the operating states of the planetary gear transmission system under the influence of different fault factors were simulated respectively. By analyzing the dynamic load spectrum and the floating trajectory of the solar wheel, the influence of fault factors on the dynamic characteristics of the planetary gear transmission system was studied. The results show that the floating trajectory of the solar wheel expands gradually with the deepening of the crack when the solar wheel has a crack fault; the amplitude of the meshing force between the planetary wheel and the inner gear ring increases slightly when it passes through the cracked gear teeth; the floating trajectory of the solar wheel instantaneously and substantially deviates at the meshing point when the broken teeth occurs; the amplitude of the meshing force between the planetary wheel and the inner gear ring is larger, and a large number of side bands appear in the low frequency region of the frequency domain diagram; the influence of fault factors on the transmission system varies with the change of working conditions.