The Diamond-Like Carbon (DLC) film, prepared with hydrocarbon gases decomposed by RF-plasma has the properties of high hardness, chemical inertness and IR transparence etc. In this paper, we study the properties of infrared, mechanical, structure and electricity of the DLC film. The spectral properties of coated element which being used in the infrared devices are presented, and the forming mechanism of the DIC film in low temperture and pressure is discussed.