Abstract: This paper touches upon that the cracked rotor is hard to detective from vibration signal and provides a solution of it from wavelet packet analysis, finds the characteristic frequency of cracked vibration by analyzing within the band where dynamic-unbalance frequencies does not exist. To deal with the defects of frequency aliasing, distortion of amplitude, and main frequency shift in Mallat algorithm, in the analysis, a new method of wavelet analysis based on frequency compensation was supplied to analyze the cracked vibration signal of shielding main pump for nuclear use, and obtain the characteristic frequency of the vibration. The results show that compared with normal wavelet packet, frequency compensation wavelet packet can recognize the characteristic frequency of vibration, and it turns out to be a quite practical method.