As an important technical means of low-NOx combustion, flue gas recirculation (FGR) technology has been widely adopted in pulverized coal boilers and chain boilers. However, in circulating fluidized bed (CFB) boilers, the stable combustion capacity under low load is seriously limited due to the conventional injection mode. In order to reduce NOx emission under the premise of ensuring bed temperature, a  new FGR method based on the synergistic effect of FGR in dilute phase zone and supplementary combustion air was proposed. The thermal experiments were carried out on a 0.2 t/h CFB combustor, and the effects of operating parameters and injection positions on combustion characteristics and NOx emission in the furnace were analyzed in detail. The key results show that the flue gas temperature in this area will decrease by 40-60 ℃, and the furnace temperature profiles will first decrease and then increase, resulting in a temperature drop of about 10 ℃ at the furnace outlet. The supplementary combustion air from the upper part of the furnace can effectively improve the gas temperature at furnace outlet. With the increase of FGR ratio, the middle FGR injection can gradually reduce the NOx emission. When the FGR ratio reaches 16%, the NOx emission can be reduced by 32% and the bed temperature is kept unchanged. With the increase of top FGR ratio, the NOx emission will decrease first and then increase. When different FGR/supplementary combustion air is sent into the top of the furnace, the mass concentration of NOx increases from 249 to 304 mg/m3 and the conversion rate of NOx increases from 17% to 33% gradually with the increase of supplementary combustion air volume and the decrease of FGR ratio. The mode of  middle FGR + top supplementary combustion air could reduce the NOx emission by 38% and maintain the combustion efficiency over 98.7%. Eventually, a NOx emission prediction model under FGR mode was proposed based on FGR injection position, excess air coefficient and FGR ratio, which could provide technical basis for better low-NOx combustion during low-load operation of CFB boilers.