According to high time-resolved lightning spectra, the evolutional characteristics of temperature and transport coefficients of the discharge channel are investigated. The results show that the return stroke channel cools down very slowly after the peak current due to the continuous heating effect of discharge current. Such a long-time continuously high temperature is one of the main causes of the lightning disasters. At the peak current stage, the heat transferring along the radial direction of return stroke channel in per unit time and per unit length of the channel is in the order of 104 J/m ⋅ s. In the meantime, the closer the distance is to the channel core, the greater the temperature gradient is, and the faster the heat transfer is from the center to outer of the channel.