Abstract: Objective The actual operating conditions of high-speed EMUs（electric multiple units） are complex, and the vibration acceleration signals of axlebox bearings often exhibit strong nonlinear and non-stationary features, with significant background noise interference. Consequently, traditional fault diagnosis methods struggle to accurately extract the fault characteristic frequencies. Therefore, it is necessary to propose a fault detection method for high-speed train axlebox bearings based on envelope synthesis. Method The detection concept of the fault detection method for high-speed EMU axlebox bearings based on envelope synthesis is elaborated as follows: First, the axlebox vibration acceleration signal is decomposed into several IMF（intrinsic mode functions） using VMD（variational mode decomposition） algorithm. Then, Hilbert transform is applied to each IMF to obtain its envelope. Next, all IMF envelopes are synthesized and reconstructed, and the reconstructed signal undergoes Fourier transform to obtain the spectrum of the vibration signal under strong background noise. Finally, a fault detection is carried out by determining whether the dominant frequency in the spectrum coincides with the fault characteristic frequency of the high-speed EMU axlebox bearings. The effectiveness and robustness of the proposed method are verified using simulated signals and actual fault bearing data from real vehicles. Result ＆ Conclusion The fault detection method for high-speed EMU axlebox bearings based on envelope synthesis can effectively reduce the influence of background noise and significantly enhance the vibration amplitude of fault characteristic frequencies in the spectrum.