Such two harmful gases as NO_x and CO produced in the sintering process of iron and steel industry will pose a great threat to the environment, and the simultaneous removal technology against them has a good development prospect. A yCu/Ti_xSn_1-xO₂ catalyst is prepared in this paper, and the technology on selective catalytic reduction of NO_x (NH₃-SCR) by ammonia is used to treat CO synergistically. The catalyst has high activity for NO_x reduction and CO oxidation. XRD, XPS, Raman, NH₃-TPD, O₂-TPD, In-situ DRIFTs and other characterization methods are used to explore the reaction mechanism of NH₃-SCR co-oxidation of CO. The results show that: the acidic site on the surface of the catalyst first combines with NH₃ to form an active substance, and then reacts with nitrate, which is in line with the Eley-Rideal (E-R) mechanism. For CO oxidation reaction, Cu can provide the adsorption site of CO and react with lattice oxygen on the catalyst surface to generate CO₂, in which the intermediate products are hydrogen carbonate and carbonate, which conforms to the reaction characteristics of MvK mechanism. The development of this catalyst has important industrial application value for ultra-low emission of sintering flue gas.