Abstract: For a thermal power plant, the continuous emission monitoring system（CEMS） was adopted to realize the measurement of carbon monoxide（CO） and oxygen（O₂） in boiler flue gas, and the air-oxygen cascade control system was designed and optimized to realize the combined control of CO and O₂. Actual application results show that this system can effectively monitor the CO content and reduce CO generated in boiler combustion. Through providing data for the boiler combustion adjustment, this system can improve the boiler efficiency, alleviate the the high temperature corrosion in boiler water wall, and improve the safety and economy of boiler operation.