The effects of different high temperature air models on electron density in the plasma sheath of the reentry capsule are studied, including the comparison between chemical non-equilibrium model and thermochemical non-equilibrium model, as well as that between 7 species model and 11 species model. The NND scheme and time preconditioning technique is applied to solve the full Navier-Stokes equations of non-equilibrium flow. Typical results of electron denstiy in the plasma sheath are obtained. The numerical results are good compared with the flight measurement and other numerical results.