The electronic structure and optical properties of undoped, Cu, I doped and Cu-I co-doped anatase phase TiO2 were calculated using the first-principles based on density functional theory.The results show that the red shift of absorption band edge can be caused by Cu, I doped TiO2 alone.For I doped TiO2, due to the interaction of the 5p orbital of I and the 2p orbital of O, the forbidden band width reduces, thus the absorption band edge is red shifted. For Cu doped TiO2, the 3d orbital of Cu introduces two impurity levels at the top of the valence band, which causes the top of the valence band to move upward. This makes the forbidden band width smaller, and the absorption band edge is significantly red-shifted.For Cu-I co-doped TiO2, Cu mainly acts at the valence band top, I mainly acts at the conduction band bottom, and then introduces impurity energy levels, so that the band gap is obviously reduced and the absorption band edge is sharply red shifted. The formation of electron and hole trapping centers by the synergistic action of Cu-I effectively hinders the recombination of electron-hole pairs and improves the catalytic efficiency for visible light.