Study of Pb_1-xGe_xTe films deposited by PVD revealed that Pb_1-xGe_xTe is a kind of fine characteristic infrared materials, which has a high transmission in the spectral range 3～ 25μm, and has indices of refraction in the range 4.8～5.6 at room temperature . Optical properties, which include transmission spectrum, dispersion spectrum and temperature coefficient dn/dT of refractive index, depend strongly on content x, environmental temperature and deposition conditions. It can be found that proper change of content x and deposition conditions may result in the change of temperature coefficient dn/dT of refractive index from negative to zero, and to positive from zero, which is of significance for manufacturing highly stable infrared optical filters.