The geometrical structures, the electronic and optical properties of anatase TiO2 doped with N, La, and La + N atoms have been investigated by using general gradient approximations plus U calculations. We explored five doping ways based on the 2 x 2 x 1 supercell of anatase TiO2. These doping methods include N-substitution of O, La-substitution of Ti, interstitial La doping, N- and La-substitutions of O and Ti, N-substitution of O, and interstitial La doping, respectively. After fully optimizing the pristine and doped structures, we calculated the dielectric functions and the absorption coefficients for all structures to evaluate the changes in the photocatalytic performance of anatase TiO2 along with different doping methods. The band energy gaps, refractive index, and photoconductivity were also calculated to provide more information for doped TiO2 application. A new effective doping approach that enhances photocatalytic performance is identified. The mechanism of the dopant-enhanced photocatalytic performance is examined with the total density of states and the partial density of states.