CO and CO₂, as important products in the combustion process, can increase the pressure of carbon reduction when they are emitted in large quantities. Therefore, high-precision real-time online monitoring of CO and CO₂ concentrations is of great significance for improving boiler combustion efficiency and accurate measurement of carbon emissions. In this work, an online measurement experimental system based on wavelength modulation direct absorption spectroscopy (WM-DAS) technology and Herriott multiple reflection cell was designed. This experimental system can achieve accurate concentrations of CO and CO₂ in mixed gases of the order of 10^-6. And the system detection limit can reach the order of 10^-8. Then, based on the experimental system, experiments were conducted to study the high-temperature catalytic oxidation characteristics of CO. The effects of oxygen content and CO concentration on catalytic efficiency were investigated. The experimental results showed that under the conditions of temperature ranging from 339 to 344 K and pressure of 101 kPa, the CO catalytic efficiency increased with the increase of oxygen content in the range of 1% to 5%. When the oxygen content was 1% and the CO volume fraction was 800×10^-6, the catalytic efficiency increased with the increase of reaction temperature. The experimental results can provide a data basis for the removal and conversion of CO in industrial flue gas.