The electronic structure and photoelectric properties of semiconductor material OsSi2 epitaxially grown on a Si(111) substrate are invesligated using the pseudo potential plane wave method based on first principles method. The calculated results show that OsSi2 is an indirect semiconductor material with a band gap of 0.625 eV. The valence band of OsSi2 epitaxially grown on a Si(111) substrate is composed mainly of Si 3s, 3p and Os 5d, and the conduction band is comprised mainly of Os 5d as well as Si 3s, 3p. The static dielectric function is 15.065, the reflectivity is 3.85, and the biggest peak of the absorption coefficient is 3.9665× 105 cm-1. Furthermore, the static dielectric function, refractivity index, reflectivity, absorption, conductivity and loss function of OsSi2 epitaxially grown on a Si(111) substrate are analyzed in terms of the calculated band structure and density of states. The results offer theoretical data for the design and application of OsSi2.