CO as an important intermediate or emission substance generated in industries such as thermal power, metallurgy, and chemical engineering, has the characteristics of flammability and high toxicity. High-precision online detection of CO is of great significance for improving boiler combustion safety and achieving carbon reduction. In this paper, tunable diode laser absorption spectroscopy (TDLAS) and Herriott multiple reflection cell are used to achieve high-precision online measurement of CO concentration in the order of 10^-6(μL/L), with a detection limit of 0.35 μL/L. In this basis, the measurement system is used to conduct experiments on the catalytic conversion performance of CO. And the effects of catalyst content and CO concentration on catalytic reactions are explored. The experimental results reveal the variation of CO catalytic conversion efficiency with catalyst content at room temperature and pressure, with a CO concentration of 10~80 μL/L, the higher the catalyst content, the higher the CO conversion efficiency. The experimental results can provide a method for removing CO from the dilution gas when measuring CO concentration using dilution sampling method, which ensures the accurate measurement of trace CO concentration.