In this research, Germanium-carbon coatings were deposited on ZnS substrates by plasma enhanced chemical vapor deposition (PECVD) using GeH₄ and CH₄ precursors. Optical parameters of the Ge_1-xC_x coating such as refractive index, Absorption coefficient, extinction coefficient and band gap were measured by the Swanepoel method based on the transmittance spectrum. The results showed that the refractive index of the Ge_1−xC_x coatings at the band of 2 to 2.2 µm decreased from 3.767 to 3.715 and the optical gap increased from 0.66 to 0.72 eV as CH₄:GeH₄ increases from 10:1 to 20:1.