Abstract: In order to control the original NO_x emission under low load of circulating fluidized bed (CFB) boiler, a 350 MW supercritical CFB boiler is taken as the research object, and the combustion process under 40% load is numerically simulated based on computational particle fluid dynamics (CPFD) method. The effects of different secondary air angles and new secondary air volumes on NO_x emissions are analyzed. The results show that with the decrease of jet angle, the NO concentration at the furnace exit gradually decreases and the CO concentration does not increase significantly. The oxygen concentration in the dense phase area of the furnace decreases after part of the secondary air is moved up, leading to increased incomplete combustion, and a more reducing atmosphere, which inhibits the NO generation. When the additional air volume increases from 10% to 30%, the NO emission concentration is reduced by 17.2%. However, as the ratio increases further, the oxygen-deficient environment in the dense phase zone of the furnace causes a decrease in combustion efficiency and a significant decrease in temperature. Therefore, the original NO emission concentration can be reduced by increasing the proportion of new secondary air without affecting the combustion.