The effects of La/Ce single-doping and co-doping on the electronic structure, differential charge density, density of states and optical properties of TiO2 are investigated based on the first principle method. The results show that, because of the synergistic action among La 5d, Ce 4f, and Ti 3d electronic states, as for the TiO2 under La-Ce co-doping, the downward shift of the conduction band is larger, the band gap is smaller, the redshift of the absorption spectrum is more obvious, and the photocatalytic performance is better than the corresponding ones under single-doping.