Abstract: To solve the problems occurring in the swirl-opposed coal-fired boiler of a 600 MW supercritical power unit, such as high and even peak mass concentration of CO in local area of the furnace, obvious deviation of CO mass concentration between left and right side along its width direction, and great changes of CO concentration under different conditions of oxygen volume fraction, etc., corresponding countermeasures were proposed by analyzing the effect of oxygen volume fraction and overfire air volume on the CO and NO_x mass concentration. Results show that the high mass concentration of CO is found to be caused by uneven air distribution, which can be improved by turning down the secondary air damper of the side air port, and the secondary and tertiary air damper of the after air port, comprehensively considering the varition tendency of CO and NO_x mass concentration, the case of φ(O₂)=3.0% is considered to be appropriate.