Abstract: When matter,especially high Z-element, is heated to high tempersture, it will be ionized many times. The degree of ionization has a strong effect on many plasma properties.So we need an approximate method to calculate mean ionization degree in many practical problems.In this paper, an analytical expression which is convenient for the approximate numerical calculation, is given by fitting it to the scaling law and numerical results of the ionization potential of Thomas-Fermi statistical model⁽¹⁾. In LTE case, the degree of ionization of Au calculated by the approximate method of Ref.(2) is in agreement with that of the averageion model. By extending the approximate method to Non-LTE case, the degree of ionization of Au is similarly calculated according to Corona model and Collision-Radiation model(C-R). The results of Corona model agree with the published data⁽¹⁾ quite well, while the results of C-R approach those of Corona model as the density is reduced and approach those of LTE as the density is increased. Finally, all approximately calculated results of ionization degree of Au and the comparision of them are given in figures and tables.