Because the working conditions of the rotate vector (RV) reducer are often reciprocating variable speed and the working environment is relatively complex, the vibration signals collected have non-stationary vibration and complex environmental noise. A fault diagnosis method for RV reducer (WDT-IF-SS-VMD) is proposed, which combines instantaneous frequency (IF) trend graph based on current signal and parameter adaptive variational mode decomposition (VMD) algorithm. Firstly, the current signal and vibration signal are collected synchronously, and the steady phase of vibration signal is intercepted based on the instantaneous frequency trend diagram of current signal. Secondly, the intercepted vibration signals were transformed into scale space (SS), and the parameters of VMD were selected adaptively based and FCM. Then, the maximum kurtosis criterion is used to complete the extraction of sensitive components. Finally, the envelope analysis is carried out to complete the fault diagnosis. The measured signal analysis results show that this method can effectively separate and extract RV reducer fault features.