Abstract: A physical model of partially ionized high-Z atoms in an intense laser field is presented, in which a spheroid distribution for the electron cloud (bound electron) surrounding the nucleus is assumed. The first and the third susceptibilities, as well as the nonlinear polarization current and the refractive index, are analytically obtained by this model. At low laser field limit, these results are consistent with that obtained from the traditional non-harmonic oscillator model, nay, the corresponding characteristic frequency of oscillator and the nonlinear coefficient can be found self-consistently from the presented model.