We calculated the band structure, density of states and optical properties of semiconductor material Ru2Si3 epitaxial-grown on Ru2Si3 （100）//Si（001） with Ru2Si3［010］//Si［110］ by using the pseudo-potential plane wave method based on first principles methods. As shown by the calculated results, orthorhombic Ru2Si3 is not only a direct semiconductor with the band gap of 0773 eV, but also in stable condition when the lattice parameter a is 1093 nm.The valence bands of Ru2Si3 are mainly composed of Ru 4d and the conduction bands are mainly composed of Ru 3d and Si 3p. Its static dielectric function ε1（0） is 1891, the refractive index n0 is 4349