There are many problems in fault diagnosis of RV reducers under variable speed conditions,such as inconsistent signal acquisition frequency,component modulation,difficulty in determining low-frequency features and frequency ambiguity,which make it difficult to extract fault features of RV reducers.In view of this problem,a order tracking analysis method for variational mode decomposition was proposed.Based on the vibration characteristics of the RV reducer,the instantaneous speed signal and vibration signal of the RV reducer were determined,and then the second-order fitting difference was performed on the speed of the RV reducer to obtain the time-speed signal.By calculating the time-speed integration,the vibration signal of the RV reducer was divided into equal angular domains,and then the target component was selected through variational mode decomposition and reconstruction,it was subjected to fast Fourier transform envelope transformation to obtain the envelope order diagram of the RV reducer fault signal.By comparing the fault order,the fault point of the reducer was determined.The proposed method can diagnose faults in situations where the acquisition frequency of vibration signal and speed do not match,solving the problem of insufficient equiangular domain division and providing a new method for fault diagnosis of complex rotating machinery under variable speed conditions.