The X-ray ionizations and the atmospheric temporal evolutions with different altitude nuclear explosions are numerically simulated in this paper. It is concluded that the density of electrons generated by X-ray ionization has a peak value at 100 ns after the X-rays have arrived, and the peak density reduced with the increase of distance from the stripped nucleus area. The life time of electrons is long, and increases with the distance from the stripped nucleus area. O+, O2+, N2+ are generated by X-ray ionization. The distance of X-ray ionization in atmosphere is within a few tens of kilometers. The peak density of explosion at 80 km high is larger than at 120 km high in the area close to stripped nucleus area, but the scenario is opposite in the area far from stripped nucleus area.