Using the one-dimensional dynamic sheath model, the effects of charging at a planar dielectric surface in plasma immersion ion implantation are studied. The temporal evolution of the sheath thickness, the effective potential at the surface of the dielectric and the ion dose accumulated on it are obtained for different plasma densities and dielectric thicknesses. The numerical results demonstrated that due to the charging effects, the plasma density has a profound impact on doping result during plasma immersion ion implantation, but the thickness of the dielectric has no significant effect on it.