Based on the first-principle, the geometrical structures, electronic structures and optical properties of FeS2 doped with and without Cu/Co are calculated and analyzed, respectively. The analysis results indicate that, as for the doped FeS2, its lattice constant increases, band gap decreases, and electrical conductivity enhances. After doping, the main peaks of imaginary part of dielectric function, absorption coefficient, and energy loss spectrum are all red-shifted, and peak values all decrease. As for co-doped FeS2, the optical transition intensity obviously enhances, and the light absorption coefficient and photoconductivity in visible region both increase, which indicate that Cu-Co co-doping can significantly enhance the photo absorption of FeS2 and increase the photoelectric conversion efficiency.