Indium tin oxide (ITO) semiconductor film is a typical wide bandgap semiconductor material. It owns much peculiarity, such as higher transmissivity in the short wavelength, higher reflectivity in the long wavelength, and super-wide reflection band, which meet the requirement of thermal photovoltaic (TPV) system. The optical properties of ITO film are calculated with the parameters of carrier concentration, mobility and thickness. The spectral curves of filters are given according to different parameters. The ITO film is prepared by using magnetron sputtering deposition technology. The optical properties of filters are given, and the ITO filter used in TPV system is prepared after anneal. The cut off wavelength of prepared filter matching with GaSb cell is 2 μm, the average transmissivity of short-wave band approaches 70%, the average reflectivity of long-wave band approaches 70%, and the ultra-wide reflection band extends to 10 μm, which can improve the efficiency of TPV system greatly.