Abstract: There is not only the small number of infrared thin films but also infrared thin films have the poor mechanical intensities,especially in mid infrared region.Reflectivities and transmittances of ZnS/Ge/ZnS,CdTe/Ge/CdTe and ZnSe/Ge/ZnSe have been computed using the theory of thin film optics.The effect of absorption and dispersion on the reflectivities and transmittances and wavelength of ZnS/Ge/ZnS has been discussed and analyzed in detail.It is shown that ZnS/Ge/ZnS has the highest transmittances and the lowest reflectivities and better mechanical intensities.ZnS films were deposited on Ge substrate using ion beam assisted deposition and the spectrum and durability has been studied and analyzed on the base of theoretical calculation of optical thin films.