In this paper, improved continuous wavelet transform is used to analyze the dispersion characteristics of a group of optical radiation signals of return stroke in an artificially triggered lightning, and the analysis results are compared with the results calculated by the classical R-L-C transmission line model. The analysis results show that the arrival time of different frequency components of the optical radiation of return stroke presents nonlinear variation with frequency. Moreover, a turning point always appears in the low frequency band on the arrival time curves of different frequency components, and the turning frequency is usually between 10 kHz and 25 kHz. The existence of this turning frequency provides a new kind of parameterization basis for evaluating the characteristic and conductivity of the return stroke channel. Based on this, the channel conductivities of the six return strokes of this triggered lightning are estimated. The average variation ranges from 0.59 × 10⁴ S/m to 0.96 × 10⁴ S/m, and the overall average value is about 0.77 × 10⁴ S/m, which are similar to the classical evaluation results.