Using the optical gas sensing materials to adsorb gases can cause the changes of the optical properties of materials. This method can be used to measure the gas composition and is a hot topic of current research in the field of gas sensitive sensors. This paper studies the micro-characteristics of rutile TiO2 (110) surface adsorption of CO molecules. By using the first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory (DFT), the adsorption energy, electron density of states, optical properties and charge density of the surface are calculated. Results show that the TiO2 (110) surface terminating in two coordinated O atoms is the most stable surface, and the structure with C-terminal of CO molecules adsorbed on the surface is the most stable. The higher the oxygen vacancy concentration, the more helpful it is to the adsorption of surface CO molecules. This process is exothermic. When the oxygen vacancy concentration is 33%, the adsorption energy can reach 1.319 eV. After adsorption, the structure of the surface tends to be more stable. Oxygen vacancy oxidizing the CO molecule is the essence of the adsorption process, and the charge of a CO molecule is transferred to the material surface. The CO molecules adsorbed on TiO2 (110) surface containing oxygen vacancies can improve its optical properties in visible light range; moreover, the higher the concentration of oxygen vacancy, the more obvious the improvement of absorption, reflection ability and optical gas sensing performance.