The first principle calculation based on density functional theory(DFT) is used in this paper to investigate the adsorption behavior of CO and Cl₂ on TiO₂(110) surface. The behavioral mechanism of the co-adsorption of CO and Cl₂ on the TiO₂ (110) surface is revealed by the calculation of the adsorption structure, adsorption energy, charge density and density of states (DOS) of the system. The adsorption of both CO and Cl₂ on the TiO₂(110) surface was mutually reinforcing, and the average adsorption energy was -1.367 4 eV, and Cl₂ could be captured by the surface Ti atom, the sd³ orbital hybridization happening on the surface Ti(5c) atom. When the adsorption reaction occurred, a transient electron flow CO→TiO₂(110)→Cl was formed on the surface. The DOS showed that the strength of Ti-O bond on (110) surface was weakened, indicating that the presence of CO has a promoting effect on the chlorination of TiO₂. Meanwhile, the surface O atoms was activated and the average energy of 1.418 6 eV was released as the dissociation of this O atom with CO from the surface to form CO₂ molecules, which destroyed the structure of TiO₂(110) and provided a good adsorption site for the next Cl₂ molecules.