Using magnetron sputtering method the Ge2Sb2Te5 films were deposited at different substrate temperatures (from room temperature to 300 oC) on Si substrate. The structure and the crystallization temperature of the films were determined by X-ray diffraction and Differential Scanning Calorimeter, respectively. The electrical resistance and the reflectivity of the films were measured with a four-point probe and ultraviolet photo-spectrometer, respectively. Based on the reflectivity of the films, it is found that the reflectivity contrasts of the Ge2Sb2Te5 films at the wavelengths of 405 and 650 nm change with the substrate temperature. The films prepared at room temperature are amorphous, and crystalline (fcc) at 140 oC, and a little hexagonal (hex) structure comes forth at 300 oC. At 140 oC the phase separation may take place, and exhibits significant influence on the electrical and optical properties.