A new approach to gear localized fault diagnosis under run-up based on angle domain average and Teager Kaiser energy operator demodulation technique is presented. The non-stationary vibration signals are transformed from the time domain transient signal to angle domain stationary one using order tracking technique. Teager Kaiser energy operator is a nonlinear operator that can track the signal energy and identify the instantaneous frequency and instantaneous amplitude of mono-component signal. The instantaneous frequency and instantaneous amplitude both exhibit a characteristic signature in the presence of a cracked tooth. The experimental result shows that angle domain average and Teager Kaiser energy operator demodulation technique can effectively diagnose gear localized crack fault.