The order tracking technique and Teager ｅnergy ｏperator (TEO) were applied to gearbox fault diagnosis during startup.Ａ met hod based on the order tracking technique, angle domain average and TEO was proposed.Firstly,the angle domain stationary signal was obtained by resampling the vibration signal sampled in the time domain. Then，the angle average and band pass filter technique ｗｅre used to eliminate the noise. Thirdly, TEO was used to track the modulation energy of band pass filtered signal and to calculate the instantaneous frequency and amplitude. In the end,the fault feature was extuacted to assess the gear damage. The experimental results show that the instantaneous frequency and amplitude both exhibit a characteristic signature in the presence of a cracked tooth.