We calculate the electronic structure and optical properties of F-doped anatase TiO2. The results indicate that the band gap ofF-doped TiO2 increases slightly compared with the pure TiO2. However, it is interesting that the visible absorption of F-doped TiO2 located between 600 and 700 nm is observed, and it enhances gradually with the increasing F concentration. Furthermore, according to the results of densities of states and imaginary part of dielectric function ε2（ω）, we propose that the transition between Ti 3d and Ti 3d states may be responsible for the visible absorption, but not the band gap narrowing.
