The backscattering factors in quantitative analysis in AES have been calculated using the "full diffusion" model which had been modified and simplified by us. Our results are quite close to the results obtained by Shimizu et al. using the complex Monte Carlo simulation, and better than the Reuter's empirical equation and Love's regression equation based on the simple Monte Carlo simulation. Our calculation are so simple that it can be applied easily in various experimental conditions without inter polation and extrapolation as used by Shimizu et al.