Ion beam co-sputtering technique is used to deposit Au-SiO2 nanocomposite films on quartz at room temperature. The nanocomposite films are annealed at different temperatures from 500～900 ℃ for 5 minutes. The film phases are identified by X-ray diffraction (XRD),the XRD spectra of Au-SiO2 nanocomposite as-deposited and annealed are obtained. Transmission electronic microscopy (TEM) is used to check Au particles distribution and size in the film annealed at 700 ℃. Optical absorption spectra are recorded in 190～1000 nm with a spectrometer. The absorption peak has a clear red-shift with increasing temperature in 500～700 ℃, and both position and intensity of the peak seem not to alter at higher temperature. It agrees well with the detection in XRD. With Drude model the absorption peak is explained theoretically.