The wavelet transform of transient signals provides a method for mapping the time domain into the frequency spectrum as a function of time. To verify the availability of wavelet transform as a time-frequency analysis tool, model experiments have been performed on the specially designed concrete lining where defects (e.g., crack and cavity) are artificially made. The stress wave is generated by dropping a steel ball and the acquired signal is analysed using wavelet transform as well as Fourier transform. It is found that the contour map by wavelet transform renders more distinct results than power spectrum by Fourier transform. The arrival time of each frequency component needed for estimation of the wave velocity can be easily determined from ridge analysis. Furthermore, the thickness of the concrete lining and the defect location can be effectively estimated using wavelet transform. Therefore, it is concluded that the wavelet transform is an effective analysis tool for detecting defect zones which exist in tunnel concrete linings.