The crystal structure, formation energy, electronic and optical properties of undoped, Co, N doped and co-doped TiO2 were investigated by first principles calculations. Considering the potential of water redox reaction of these systems indicate that only N-, Co-1N- and Co-2N co-doped TiO2 meet the requirement of the photosplitting water. Moreover, the optical absorption threshold and absorption area of Co-2N co-doped TiO2 are obviously enlarged compared with the undoped TiO2. Co-2N co-doped TiO2 has the highest light absorption efficiency and hydrogen production efficiency, due to the presence of curved and broad impurity levels that greatly improve the carriers' mobility and separation. (C) 2017 Elsevier B.V. All rights reserved.