The crystal structures, electronic structures and optical properties of pure and nonmetal (B, C, N, F, P, S and Cl) doping anatase TiO2 were calculated by the first-principles based on the density functional theory with the plane-wave ultrasoft pesudopotentials method. The calculated results show that the octahedral dipole moments of TiO2 are increased by nonmetal doping owing to the changes of lattice parameters, bond length and charges on atoms, which is very effective for the separation of photoexcited electron-hole pairs. Because the impurity energy levels are formed by hybridizing with dopants’ p states, O 2p states and Ti 3d states, most dopants could narrow the band gap, resulting in its fundamental absorption edge red-shift to visible-light region. According to the calculated results, the effects of nonmetal doping on electronic structure and optical properties of anatase TiO2 were analyzed and compared, and the roles of nonmetal atoms in TiO2 photocatalyst under visible-light irradiation were clarified. The calculated results could explain the reasons that some nonmetal-doped TiO2 have higher photocatalytic activity under visible-light irradiation.