Abstract: A new approach to non-destructive measurement of pod weight based on sound was put forward. The signal processing method using wavelet packet transform to extract the key features from sound was studied. The noise signal in every frequency band was received after noise signal was decomposed by using wavelet packet. Then the energy spectrum in every frequency band was regarded as the eigenvalues of discerning silkworm chrysalis weight. Experimental results show that the application of wavelet packet to extracting energy spectrum is valid and feasible, and the method also solves the difficult problem in the process of non-destructive mearsurement of pod weight.