An improved envelope analysis approach based on spectral kurtosis (SK) and complex shifted Morlet wavelet in the diagnostics of local gear faults is proposed in this paper. For enhancing impact signals of gear faults, a prewhitting process is performed to the original signals by autoregressive (AR) models firstly in the approach. Then, the envelopes of signals are extracted by Morlet wavelet filter family and the optimal center frequency and bandwidth of the band-pass filters is determined by SK. In the improved approach, not only the optimal parameters of the band-pass filters in envelope analysis can be obtained adaptively by, but also the number of the required band-pass filters can be reduced dramatically. Simulation results verified the feasibility of the present scheme positively.