We have calculated the electronic and optical properties of Eu-doped, N-doped, and (Eu,N)-codoped TiO2 using plane-wave pseudopotential method based on the density functional theory. The calculated results show that there are impurity levels of Eu 4f appearing in the band gap of Eu-doped system, and N-doped system can lead to narrowing of the band gap. Moreover, the synergistic effect of the Eu and N codoped TiO2 leads to the lattice distortion and band gap narrowing. Optical absorption curves indicate that the (Eu,N)-codoped system exhibits a significant red-shift of absorption edge, which enhances the visible-light photocatalytic activity.