GeC thin films were deposited on ZnS substrates with reactive RF magnetron sputtering, and the influences of the processing parameters on sputtering of the Ge target and IR transmission properties of the GeC films were studied. At low substrate temperatures, the GeC film contained H atoms in forms of CH2，CH3 and Ge-CH3 groups, which caused IR absorption, whereas the absorption decreased obviously at elevated substrate temperatures. Target-substrate distance, RF power, Ar:CH4 gas flow ratio and total gas pressure had great impacts on the poisoning and sputtering of the Ge target, but their impacts on the IR absorption of the GeC film was small. When the Ge target was poisoned greatly, adhesion of the GeC film was inferior, with the weakening of the target poisoning, adhesion of the GeC film increased. Hydrogen-free GeC film with excellent adhesion was prepared on ZnS substrate under optimized parameters, and its refractive index was about 1.78. The C content in the GeC film was larger than the Ge content, and C and Ge formed mainly C—Ge bonds. GeC/GaP antireflective and protective film system was prepared on ZnS substrate, giving good antireflective effect.