The design of film system for obtaining a-C:H films on Ge single crystal withantireflective or simultuncouslly antireflective effect in both single band (3~5 μm) anddouble bands (3~5 μm and 8~12 μm) was studied. The analysis of the antireflectiveeffect of these films with the aid of a ellipsometer was discussed. The results show that a C:H film could be used as an ideal IR antireflection material. It was also found thateilipsometry analysis was essential for both studying on it the films will or will not be in accordance with the film system design and determining the deposition conditions.