In recent years, many theoretical and experimental researches have reported that different atoms doping TiO2 is one of the effective methods to reduce the gap. In this paper, the band structure, density of states and optical property of C-Zn co-doped rutile TiO2 are studied by the plane-wave ultrasoft pseudopotential method based on the first-principles density functional theory. The calculations show that C-Zn co-doped TiO2 results in the conductor band apparently shifted down to the Fermi level. Some impurity energy levels of co-doped TiO2 are below the conduction band minimum, and others are above the valence band maximum. The distance between them narrows down, which results in the redshift of the optical absorption edges to visible-light region. These impurity energy levels can reduce the recombination rate of photoexcited carriers and improve the photocatalytic efficiency of TiO2. Besides, the optical absorption coefficient becomes larger in visible-light region and the energy loss decreases clearly.