The prospects of Si-based optical emitting materials are optimistic because the materials are compatible with silicon microelectronics technology. Therefore, many experimental and theoretical studies are directed to the design of direct band-gap Si-based materials. Based on the core state effect, the electronegativity differences effect of component atoms and the symmetry effect, Si-based superlattices Si1－xSnx/Si were designed. We found that Si0.875Sn0.125/Si is a direct band-gap material. In the density functional theory frame, the results of plane pesupotential method show that Si0.875Sn0.125/Si is a direct band-gap superlattice with minimum band-gap at Γ point. We predict that the band gap of the material is 0.96 eV with the help of GW approximation method.