Tin oxide has become one of hot points in transparent conductive materials due to its excellent electrical and optical properties. Based on the full-potential linearized augmented plane wave method (FP-LAPW), we investigate the electronic structure and the optical properties of the material Fe-S co-doped SnO2. The results show that the two co-doped compounds are all direct transition semiconductors with half-metallic properties. Fe-S co-doping can narrow the band gap, and the density of states (DOS) shifts toward the low energy with the increase of S concentration. The charge density of co-doped system is redistributed, and the degree of Fe polarization and the capacity of bonding are enhancd with the increase of S. What is more, the peaks of imaginary part of dielectric function and optical absorption are red shifted, and the absorption edge decreases with the increase of S concentration.