The figure shows the frequency domain diagram of bearing 1 and bearing 3 when root crack and outer raceway fault of rolling bearing occur simultaneously. The main frequency components in figure (a) are the bearing outer raceway fault frequency⻕0 (107.3hz) and its multiple frequency; the meshing frequency of the fault gear⻕m (570.4hz); in addition, there are other characteristic frequencies 85.25hz and their multiple frequencies. Through calculation, it can be known that 85.25hz is the double frequency of the failure frequency of bearing 3 outer raceway, because the characteristic frequency of bearing 3 is transmitted to bearing 1 through the system Yes. Comparing the fault frequency of raceway with the theoretical value, it can be found that the difference between them is very small, which can prove the correctness of the system model. The main frequency components observed from figure (b) are: frequency doubling of outer raceway fault frequency of bearing 3, outer raceway fault frequency of bearing 1 and meshing frequency of faulty gear.