Abstract: The specimen which was made up of composite shell and adiabatic layer was tested by AU technique. The noise in the tested signal was reduced by adaptive filtering, multi-resolution analysis of the signal was achieved by wavelet transform in the experiments. On the basis of the energy ratio of the signal in different frequency zones, the characteristic frequency zone of the signal was gained. The characteristic frequency zone of the signal from specimen was evaluated by energy integral stress wave factor(SWF). The porosity-type defect was found effectively, and the size of defect could be evaluated qualitatively. The validity of AU test for bond quality of SRM structure is approved in the experiments.