Using the first principle plane- wave pseudo potential method, a systematic investigation on electronic and optical properties of ZnS with and without La-doping has been performed. Calculation results show that La-doping narrows the band gap of ZnS systems and La doped ZnS system changes from semiconductor into metal through the Mott transition. Moreover, with La-doping increasing, the decrease of absorption coefficient and redshift of absorption spectra are obtained. Absorption spectra of pure
