The electronic structure and optical properties of intrinsic and P, As doped Mn4Si7 were calculated with the fisrt-principles calculation method. The result shows that the intrinsic Mn4Si7 is an indirect semiconductor material with a gap of 0.810 eV, the P doped Mn4Si7 band gap increases to 0.839 eV, and the As doped Mn4Si7 band gap decreases to 0.752 eV. Doping causes a shift to the low energy region, and causes an increase of the real part of dielectric function notably in the low energy region and an increase of the imaginary part in almost all region, imaginary part decreases to zero after 8 eV. Besides, doping obviously increases the extinction coefficient, absorption coefficient reflection coefficient and photoconductivity in the high energy region, and improves the optical properties of the Mn4Si7.