The propagation characteristics of the return-stroke current wave along the channel are an important issue in lightning research. The temperature, electrical conductivity and radius of lightning dart‑leader channels were calculated based on spectral diagnosis. Using them as initial parameters the dispersion equation for electric wave propagating along the return-stroke channel in a wide angular frequency range was solved numerically. The dispersion relations for the electric wave with and without considering the corona sheath effect were investigated. The results showed that both the propagation velocity and amplitude of electric wave decay along the channel, and the high frequency components decay faster. The corona sheath hastens the attenuation of the electric wave. The peak current intensity is closely related to the physical characteristics of the leader channel and determines the propagation velocity and amplitude attenuation of electric wave. Inferred from the attenuation characteristics of the wave, the variation of the current intensity along the channel is mainly determined by the different attenuation rate of the harmonic components with different frequencies during the transmission process.