The three-layer-film model for SnO2:F film with chorionic surfaces is suggested. Using the matrix of interface and the layer matrix representing the properties of propogation of plane waves, we have deduced the scattering matrix and the overall reflection coefficient of the three-layer structure and obtained the basic formula of the reflection ellipsometry. The dispersion relation and thickness of SnO2:F films with chorionic surfaces have been measured by using the spectroscopic reflection ellipsometry.