The microstructures and optical properties of N and Co-codoped anatase TiO2 are investigated by using the plane-wave ultrasoft pesudopotential method of first-principles. The calculated results show that the octahedral dipole moment of anatase TiO2 increases after N and Co codoping, which is favorable for effective separation of photogenerated electron-hole pairs. Some new impurity energy levels of codoped TiO2 appear between the conduction band and the valence band, which results in the red shift of the absorption wavelength toward visible-light region and an apparent increase in performance of light absorption. These impurity energy levels can promote the effective separation of photogenerated electron-hole pairs, which facilitates the improvement of the photocatalytic efficiency of codoped TiO2. The band edge redox potential of codoped TiO2 is only slightly changed compared with that of pure TiO2, which means that the strong redox capacity of codoping photocatalyst is still excellent.