By using pseudo-potential plane-wave method of the first principle based on the density function theory, geometrical structure, electronic structure and optical properties of Al-doped CrSi2 are calculated and analyzed. The calculated results on geometrical structure and electronic structure show that the lattice constant a and b increase while c has little change, the volume of lattice expands, the band structure is still indirect and the Fermi energy moves into the valence band deeper and deeper with Al increase from 0 to 0.3333, the density of electronic states near the Fermi energy level is mainly composed of Cr-3d. Optical properties calculation indicates that after doping Al, static dielectric constant, the first peak of ε2(ω) and refractive index n0 increase, the average reflective effect decreases, the light absorption of CrSi2 effectively enhances, and then improves the photoelectric conversion efficiency after doping Al. These results offer theoretical guide for design and application of optoelectronic material of CrSi2.