Pt/TiO₂ catalyst has been used for catalytic oxidation of CO in the environment, and many progresses have been made in the treatment of CO emission from industrial gas. Pt/TiO₂ catalysts doped with different Se contents are prepared, the structure and microscopic morphology of Pt/TiO₂ catalysts are studied by SEM (EDS) and XRD detection, and the elemental valence state on the surface of the catalysts are studied by XPS, CO-TPD and H₂-TPR detection methods, and the influence mechanism of Se doping on the performance of Pt/TiO₂ catalysts is summarized. The results show that Se doping promotes electron transfer in metal-support, increases Ti³⁺ and oxygen vacancies, and is conducive to the flow of reactive oxygen. At the same time, the Se doping enhances the strong metal-support interaction (SMSI) effect of the catalyst, promotes the movement of electrons from Pt to Se, increases the valence state of Pt, increases the content of PtO_x in the active site, and increases the reactive oxygen of the reaction. The results of catalytic performance test show that when the Pt/TiO₂ catalyst is doped with 0.1% Se, it gets the best CO catalytic oxidation performance.