The optical properties of vanadium oxide thin film are measured at semiconductor-metal transition, including reflectance and transmittance results at different wavelengths which show different trends during the phase transition. With a multi-level reflection-transmission model of incoherent light, we calculate the values of refractive index n and extinction coefficient k at different wavelengths, and show that the abnormal optical properties result not only from the dependences of n and k on the wavelength, but also from multiple reflections in the absorbing film.