The optical properties of amorphous Ge_xAs_xSe _2-x (x=0.05÷0.30) thin films prepared by thermal evaporation on the glass substrates held at T_substr=100 °C are reported. The transmission spectra was used for calculation of the absorption coefficient α, optical band gap E_g, and the values of the refractive index n. The dependences of α, E_g, and n on the film composition in the Ge_xAs_xSe_2-x glassy system were determined. It was established that the optical band gap E_g decreases, while the refractive index n increases with the increasing of the concentration of Ge and As in the Ge_xAs_xSe_2-x glassy system. The time dependence of the transmission T(t) during the light exposure for the above band gap illumination (photodarkening) is described by a strength exponential behaviour T(t)/T(0) = A₀+Aexp[-(t-t₀)/τ] ^(1-β), where t is the exposure time, τ is the apparent time constant, A characterizes the exponent amplitude, t₀ and A ₀ are the initial coordinates, and β is the dispersion parameter (0<β[removed]