Abstract: Based on the nonlinearity and nonstationarity of vibration signal of aero-engine rotor, Fourier decomposition method (FDM) is applied to the diagnosis of composite faults of aero-engine rotor. First, the vibration signal was decomposed into several Fourier intrinsic band functions (FIBFs) by FDM. Then the kurtosis value of each FIBF and the cross-correlation number between each FIBF and the source signal are calculated of each FIBF. The main FIBFs are extracted and the signal is reconstructed by combining the cross-correlation number threshold and kurtosis threshold. According to the main FIBFs, the marginal spectrum is generated to realize the analysis of the main spectrum components. Finally, the harmonic component and impulse component of the signal are extracted by combining the cross-correlation number and kurtosis value, and the composite fault can be further judged and analyzed. This method is applied to the diagnosis of the composite fault signal of the aero-engine rotor tester, and the fault features of misalignment, looseness and rubbing are separated. It is proved that this method can realize the feature separation and diagnosis of the composite fault.