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.