Abstract: Since the velocity of the spacecraft in cold and dense plasma is larger than local ion velocity but more smaller than electronic velocity,the electrons could more easily move into the wake area and consequently form a high negative potential barrier,which produces wake charging effect.Especially in Polar Earth Orbit(PEO),where exists energetic auroral electrons injection,the dielectric materials in the wake area can be charged to high negative potential.In this paper the physical mechanism of wake charging effect were analyzed,and the physical model was established by using of double Maxwellian distribution of energetic aurora electrons and accounted the effect of the background plasma and secondary electrons.