Abstract: Gear tooth crack fault signals are very feeble when the crack is in early stage.To extract early gear tooth crack fault feature effectively,the paper puts forward a comprehensive demodulation analysis method. The method integrates the amplitude-envelope demodulation and the phase-demodulation analysis to the character of the concurrence of amplitude-modulation and phase-modulation in actual gear vibration signals.Simulation results and actual diagnosis example demonstrate that the comprehensive demodulation analysis method proposed in this paper can extract the early crack fault feature of gear from complicated vibration signals and increase the fault diagnosis precision ratio.