The high quality vanadium dioxide (VO<sub>2</sub>) thin films have been fabricated successfully on sapphire by a simple novel sputtering oxidation coupling (SOC) method. Transmittance spectra of vanadium dioxide film have been measured between 25 °C and 90 °C. The thin film samples exhibit a good insulator-metal transition near room temperature. The optical constants of VO<sub>2</sub> thin film samples were derived by fitting the transmittance spectra using the Drude-Lorentz model. In order to improve the transition efficiency, the thin film thickness was optimized by the optical design. The calculated results with different thin film thickness show that VO<sub>2</sub> thin film with 84 nm owns a maximums value of the transition efficiency. This research will promote VO<sub>2</sub> thin film optical performance improvement for the smart windows.