Abstract: With the improvement of environmental protection standards,NO_x emission control of power plant boilers is increasingly strict.Low-NO_x retrofit can effectively reduce NO_x generation,but the research on combustion characteristics in low load after retrofit is limited.The combustion characteristics of a 300 MW low-NO_x retrofitted tangentially-fired boiler under low load and multiple operating conditions were numerically simulated in this work. The influence of excess air ratio,burnout air ratio and pulverized coal feeding rate of primary air nozzle on the velocity,temperature and species distributions in the furnace were studied. By improving the grid system,the accuracy of simulation results is improved. The deviation between the simulation results and the experimental measurements is small,which shows that the simulation results are reliable. The results show that with the increase of excess air ratio,the temperature rises up,the reducing species decrease and the NO_x emission increases. When the excess air coefficient increases from 1. 20 to 1. 30,the NO_x emission increases from 221.12 mg/m~3 to 196.26 mg/m~3. With the increase of burnout air ratio,the temperature of the main combustion zone decreases,the temperature of the burnout zone increases. The reduction of the temperature of the main combustion zone inhibits the generation of thermal NO_x ,and the NO_x emission decreases. When the burnout air ratio increases from 20% to 30%,the NO_x emission decreases from 231.21 mg/m~3 to 180.95 mg/m~3. The influences of pulverized coal feeding rate for primary air nozzle on temperature,species concentration and NO_x emission are small.