Abstract: In order to investigate the effect of the nonlinear atmospheric electric parameters at high altitudes on the propagation of lightning return stroke electromagnetic field, the upper troposphere atmospheric electric-coupling model is performed by using the 2D Finite-Difference Time-Domain method, considering the electronic thermal effect, ionization and absorption effect in the Maxwell's equations. For the lightning return stroke field within the initial microseconds times, our simulated results show that the effect of the nonlinear atmospheric electric parameters below 60 km altitude can be ignored while it has to be considered above 60 km altitude, because the relaxation time below 60 km altitude is about several milliseconds, however, it is less than 1 ms above 60 km altitude. It is found that the nonlinear effect of the atmospheric electric parameters reduces the vertical field peak value more significantly than the horizontal electric field, and the peak value of the vertical electric field can be reduced by 75% or so. Because the vertical electric field lasts hundreds of microseconds while the horizontal electric field is only tens of microseconds, the longer the time of the field pulse continues, the more attenuation of the field peak will be made due to the relaxation time within several microseconds.