Bond formation and relaxation are effective methods to alter the electronic and photonic behavior of semiconductor. With the aid of first principle calculations, the electronic properties of TiO 2 have been modulated by the impurity C, Fe, Co or H atom. Results show that, the electronic distribution around the impurity atoms is changed by the bonds formation and relaxation. The electronic and photonic behavior of TiO 2 based photocatalysts are altered by modulating the number and energy of impurity level and reducing the band gap. Moreover, the carrier mobility in impurity levels increased after the H atom being introduced into, which not only reduce the electronic transition energies but also suppress the electron–hole recombination rate. Finally, the Co-C-2H codoped TiO 2 may have the best photocatalytic activity.