Copper thin films are deposited on K9 optical glass substrate by magnetron sputtering method. By X-ray diffraction, the structure of copper film are detected. By Ultraviolet (UV)-visible spectrophotometer and grating spectrometer, the optical absorption properties of copper film are detected. The results show that: for the same Cu thin films, the peak-number and peak position obtained by two different instrument are different. The peak of absorption spectrum is two obtained by grating spectrometer and has a "red shift" to that obtained by UV-visible spectrophotometer, this due to the different instrument resolutions and different light sources.