A simple classical treatment of the potential curve fitting to the experimental differential cross section is presented. The classical deflection function is expanded in a triple series of the inverse power of the impact parameter. This series holds for any combinations of both repulsive and attractive inverse power potentials stronger than γ-2, and it permits an analytical evaluation of the classical differential cross section. This method is attempted to fit to the differential scattering data of Ar++Ar and Xe++Xe measured by Lorents, Olson and Conklin. Results show fairly good agreement in the neighborhood of the rainbow scattering angle except for the oscillatory interference patterns due to the resonant electron exchange. This method is simple and it may save much numerical labour compared with semiclassical or quantal treatment.