Dispersion is the intrinsic characteristic of Lamb waves, which influences the effective applications of Lamb waves in plate-like structures. The continuous wavelet transform (CWT) was applied to the Lamb wave signals with narrow frequency band captured from aluminium structures. The CWT-based contour and ridge were therefore searched in the time-scale domain. The unavoidable dispersion characteristic was used in this paper to distinguish the mode of each wave package and pinpoint these packages at each scale for determining the actual group velocities of dispersion curves. Analysis results demonstrate that the proposed approach is effective in dispersion analysis and wave mode differentiation.