Abstract: In this paper, the effects of the height of channel, the return stroke speed and the permittivity of ground on the return stroke radiation field are discussed based on TL, MTLL, MTLE, TCS and BG model. Assuming a common current wave shape at the channel base, the electromagnetic field have been calculated under different conditions. The calculating results show that the height of channel doesn't affect the field before the current gets to the channel end. The initial peak of electromagnetic field increases with increasing return stroke speed, same as the high frequency component of electromagnetic field at close range. The permittivity of ground affects the initial peak and the wave tilt of fields.