In order to overcome the defect that the frequency domain was divided by the dyadic mode in the traditional harmonic wavelet packet, an improved harmonic wavelet packet that could divide the frequency domain more finely was proposed. In order to overcome the defect that the parameters of bandpass filter were selected by the experience of the user in the conventional envelope analysis and enhance the performance of kurtogram, by combining the improved harmonic wavelet packet with kurtogram, the improved harmonic wavelet packet kurtogram was given, based on which a method to diagnose the mechanical fault was presented. The simulation and fault signal analysis show the method overcomes the defect in the conventional envelope analysis and enhances the performance of kurtogram.