96%。 A singularity indicator of time-domain pulse response signal, related with the singular intensity and frequency band, was presented by using wavelet transform modulus maxima, in which the response signal has been detected by a mini-microphone and sound adapter when egg-shell was excited with a mechanical impact. The analysis showed that the most singularity indicators of the cracked eggs only located in the low-frequency bands with big indicator values, meanwhile those of the intact eggs were found in the more frequency bands with small indicator values. A standard value, as singular indicator was defined with weighted average value, and a multi-level scheme for egg-shell crack detection has been proposed. Test results with 96% recognition ratio showed the efficiency of the proposed multi-level detection method.