The catalytic reaction between CO and NO on polycrystalline Pt surface, which is very important in the development of catalyst for automobile exhaust gas control, has been studied using thermal desorption spectrometry(TDS) and steady-state experiment under ultra-high vacuum(UHV) conditions. With the pressures of CO and NO of each 1×10^-7 Torr, the CO₂ formation rate showed a maximum at 560K. At the reaction temperature of 560K and the NO pressure of 1×10^-7 Torr, the production of CO₂ was first order in CO₂ was first order in CO pressure below 1.35 × 10^-7 Torr of CO pressure whereas at higher CO pressures the rate became minus 0.3 order in CO. But the efforts of reactant pressure on the reaction was understood in consideration of the surface concentrations of adsorbates. With the results, we proposed a new reaction mechanism for this reaction.