Abstract: In order to reveal the operating characteristics of circulating fluidized bed under different loads, a 660 MW circulating fluidized bed boiler was taken as the research object. Under full load and 75% load, the effects of bed temperature fluctuation, air volume ratio, flue gas oxygen content and air-coal ratio on ammonia injection and denitrification effect of selective non-catalytic reduction technology were studied. The results showed that during full load operation, the ammonia injection projected by SNCR maintained the same trend as the coal feed of the circulating fluidized bed boiler in the oxygen deficient zone. If the ammonia injection is continuously increased, it would lead to significant ammonia escape and reduce the SNCR denitrification capacity. If the coal feeding amount remained stable in the furnace, increasing the secondary air volume（oxygen content） in the oxygen deficient reduction zone appropriately would promote the reduction reaction of volatile nitrogen. During 75% running load, to meet the denitrification requirements, when the bed temperature fluctuation exceeds 110 ℃, it was necessary to increase the primary air volume, reduce the secondary air volume and spray ammonia appropriately. When the bed temperature fluctuation was below 50 ℃, the primary air volume and ammonia injection amount should be decreased appropriately. If the fluctuation range of bed temperature was higher than50 ℃ and lower than 100 ℃, the secondary air volume and ammonia injection amount should be reduced appropriately. In the oxygen deficient zone, the ammonia injection amount was increased when the total coal amount was increases.The research results can guide the optimal operation of circulating fluidized bed to reduce nitrogen oxide emissions.