According to the theory that there is an injection of the rotor imbalance fault space into rotor induced fuselage vibration space, the experimental data are obtained through the imbalance settings of mass and aerodynamic parameters (pitch and trim tab) on a helicopter rotor test rig. Based on wavelet transform and neural network, the diagnosis of helicopter rotor single and compound imbalance faults is carried out by using the fuselage vibration signal. The method is given for diagnosing rotor imbalance fault by processing fuselage vibration signal with wavelet transform. 