Ceria supported platinum catalyst has now been widely studied due to its excellent activity for CO oxidation. However, the electron state of active metal center is still an open question. In this work, a ceria nanorod support was prepared and platinum (Pt) with 0.9 at％ was deposited using an impregnation method to obtain Pt/CeO2 catalyst. With the help of“light-off”experiment and temperature-programmed reduction under CO (CO-TPR) test, the conclusion is proposed that the process of hydrogen reduction can enhance the activity of CO oxidation reaction for the generation of optimal active Pt site. An innovative near-situ X-ray absorption fine structure (XAFS) technique was used to investigate the chemical state of central Pt atom during the reaction process, clearly demonstrating that the high oxidized state of Pt does harm to the activity for CO oxidation while the relatively reductive Pt exhibits high activity, and the different oxidized state and chemical environment of Pt during every process has been identified. Furthermore, the activity of our Pt/CeO2 catalyst is superior to that of most of the pre-vious reports about CO catalytic oxidation by Pt based catalyst. Moreover, the optimal active species (Pt-O4) have been identified after hydrogen reduction, which could be a possible key strategy to control the oxidation of Pt.