In order to study whether tin doped CuS could be used as counter electrodes for dye-sensitized solar cells, first-principles were used to calculate the electronic structure and optical properties of it. The calculated results show that tin ions can substitute two different kinds of copper ions in the supercell of CuS, and they demonstrate different properties. The calculated results of electronic structure indicate that the introduction of tin ions change the conductive properties of CuS counter electrode. The calculated results of optical properties indicate that the introduction of tin ions change the optical properties of CuS counter electrode, and tin doped CuS could be excellent counter electrodes for dye-sensitized solar cells.