Abstract: Three methods were discussed which were wave velocity method, two-dimensional Fourier transform method and smooth pseudo Wigner-Ville distribution. The experiments were carried out on aluminium plates, and the single and multimode Lamb waves because of its nature dispersion were excited by 5 MHz oblique incidence longitudinal wave in 0.82 mm and 1.32 mm thick plates respectively. The results of these methods showed that wave velocity method was effective for single mode Lamb waves, while the other two methods were able to identify multimode, furthermore, smooth pseudo Wigner-Ville distribution could give the information of position of different Lamb wave modes in time domain. In practice, two-dimensional Fourier transform was suit for automatic scanning, and smooth pseudo Wigner-Ville distribution should be used in the case where there was no real time required.