In order to intuitively reflect the differences between the radii of the earth ellipsoid in high-precision navigation and positioning calculations, analyze the change and difference values between earth radius vector and radius of curvature of normal section by using the computer algebraic system. The results show that as the latitude of the earth increases, the difference values between the radius of curvature of the normal section continue to decrease and are equal at the poles; In short distance plane calculation, the radius of curvature at can be approximated regarded as the average radius of curvature ; The extreme values of the difference between the earth radius vector and the commonly used radius of curvature are located at the equator or at the pole. The difference curves between the radii of various earth ellipsoid derived and analyzed intuitively display the difference values between the earth ellipsoid radius vector and the radius of curvature of the normal section, providing a theoretical and numerical basis for the error impact caused by the selection of the radius of the earth model in navigation and positioning calculations.