The first-principal pseudopotential plane wave method based on density functional theory was used to calculate the geometrical structure, electronic structure, complex dielectric function, absorption coefficient and photoconductivity of Sc or Ce doped and co-doped CrSi2, respectively. The results show that the lattice constants of CrSi2 increase with the doping of Sc and Ce, and the values of bandgap decrease with the co-doping of Sc and Ce. The band gaps of Sc, Ce and co-doped CrSi2 decrease to 0.245 eV, 0.232 eV and 0.198 eV, respectively. The Fermi level of doped CrSi2 moves to the low energy region and enters the valence band. Due to the major contribution of the 3d state electrons of Sc and 4f state electrons of Ce, the single Sc or Ce doped CrSi2 appears an impurity level below the conduction band. Sc-Ce co-doping makes CrSi2 transform into metal, and the electrical conductivity is improved obviously. After doping, the first dielectric peak of the imaginary part of the CrSi2 dielectric function increases and moves towards the direction of low energy, indicating that Sc or Ce doping enhances the optical transition intensity of CrSi2 in the low energy region, and great intensity is obtained when the CrSi2 is co-doped by Sc-Ce. The absorption edge of Sc or Ce doped CrSi2 redshifts in the low energy direction. The intrinsic CrSi2 hardly absorbs photons when the photon energy is greater than 21.6 eV, especially near higher photon energies at 31.3 eV. The absorption ability of Sc doped and Sc-Ce co-doped CrSi2 increases, and the second absorption peak is formed near E=31.3 eV. The results show that doping Sc or Ce can improve the absorption of CrSi2 to infrared and higher energy photons. The photoconductivity of CrSi2 increases after doping in the low energy region of less than 3.91 eV. In the energy range of 20.01 eV