In order to provide more accurate theoretical guidance for the improvement of photoelectric properties of chalcogens doped silicon, the lattice structure, stability, band structure, density of state and optical properties of (S, Se) co-doped silicon were systematically investigated based on the first principles, and the related properties were compared with those of S-doped and Se-doped silicon. The calculated results show that the photoelectric characteristics of S-doped Si and Se-doped Si are extremely similar, with a new impurity band appearing in their bandgaps. This new impurity band is primarily due to the contribution of the 3s state electrons of S and the 4s state electrons of Se, promoting the absorption of low-energy photons and increasing the optical absorptivity of doped Si in the near infrared region. Compared with monocrystalline silicon, the optical absorption spectra of S-doped Si and Se-doped Si show a new peak at 0.6 eV, which is caused by the transition of electrons from the impurity band to the conduction band. (S, Se) co-doped Si exhibits good stability at operating temperature; and two impurity bands appear between the valence band and conduction band, which are formed by electrons from the 3s state of S and the 4s state of Se, respectively. The optical absorptivity of （S，Se）co-doped Si is greatly improved in the low energy region compared to that of single doped Si, with a new absorption peak appearing at 0.65 eV, similar to the formation observed in singly doped Si. However, due to the indirect transition process between two impurity energy bands, the absorption peak of (S, Se) co-doped Si is larger in the low energy region. Compared with S-doped silicon and Se-doped silicon with the same concentration, the optical absorptivity of the (S, Se) co-doped is significantly improved in the range of 0.81 eV to 1.06 eV. This study provides theoretical guidance for (S, Se) co-doped Si in the field of photoelectron such as infrared photodetectors and solar cells.