The elastic cross sections of e^--He and e^--Ar col1isions are calculated using Roothaan-Hartree-Fock wavefunctions in a model potential scheme，including static，stater's type exchange and polarization potentials. The calculations agree with the experimental data. By comparing our calculations and the emperical exchange parameter used in the calculations with those of other authors' by using different atomic wavefunctions，the effect of the difference of different approximate atomic wavefunctions on the calculations is investigated.