Abstract: The charge-neutralization processes of the initial stage for IREB propagationin a metallic drift tube filled with low-pressure neutral gases are simulated byMonte-Carlo method, The physical processes considered are comparatively complete.The simulation results agree to experiments and confirm that ion impact ionizationeffects play a crucial role in establishing charge-neutralization and that secondaryelectron effects are not important in the charge-neutralization processes of theinitial stage for IREB propagation.