Optical properties of monolayer oxygen-doped Ge-Sb-Te thin films prepared by RF-sputtering method were studied in the region of 400 nm～800 nm, including refractive index, extinction coefficient, reflection and transmission spectra. The results indicated that larger reflectivity contrast can be achieved by appropriate doping of oxygen, thus the recording properties of the Ge-Sb-Te film material can be improved by the oxygen-doping.