Diamond-like carbon (DLC) i.e.amorphous carbon films were grown on germanium (Ge) substrates by rf-plasma decomposition of methane.Fourier transform infrared (FTIR) spectroscopy measurement showed that the DLC films acted as the anti-reflect coatings of Ge substrates,especially,maxima of the transmission of DLC/Ge/DLC were above 99% from 1740 cm-1 to 2044 cm-1,94.5% at 945.7 cm-1(10.6 μm).IR transmission spectroscopy and improved transmission formula were used to calculate the absorption coefficient of DLC films from 2.5 μm to 12 μm.The results indicated that the absorption coefficient of the films approached 0 ranging from 1700 cm-1 to 2600 cm-1 and 230 cm-1 at 945.7 cm-1.The sp3 C-H bonds were dominate in the DLC films.All the absorption peaks were well explained by bonds.