The electronic structures and optical properties of Sb-doped SnO2 are studied by first principle calculation based on density functional theory (DFT). The computed results show that, with the increase of Sb doping concentration, the Fermi energy level passes through conduction band, and the band gap is narrower in succession, meanwhile, the energy level of shallow donor impurity is shifted away from the conduction band bottom, which makes the conductivity enhanced. The calculated results of charge density indicate that Sb-doping can change the property of SnO2 bond formation, which makes the covalent weakened and the metallicity enhances with the increase of Sb doping concentration. The calculated results of optical properties show that the imaginary part of the dielectric function has a red shift like the total density of state (TDOS) with the increase of Sb doping concentration, which indicates the internal relationship between electronic structure and optical properties theoretically.