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