Abstract: In the context of deep peak shaving, existing coal-fired power units often need to operate at low loads. The simulation and on-site experimental research on the combustion and NOx emission characteristics of a 1000 MW double tangential boiler under low load were conducted. The consistency between simulation and on-site test results is good. The numerical results indicated that under low load, the carbon content of fly ash is the highest under the pagoda-type air distribution mode, while the carbon content in fly ash was the lowest under the shrunk-middle-type and equal-type air distribution modes. However, the difference in NO concentration at the boiler outlet was relatively small under the four air distribution modes. BCD mills combination model had the lowest carbon content in fly ash and the highest NO concentration, while DEF mills combination model had the highest carbon content in fly ash and the lowest NO concentration. When the over-fire air rate was 15% and 20%, the carbon content in fly ash remained around 1.0%; as the over-fire air rate increased to 25%, the carbon content in fly ash increased significantly, 2.5%. NO concentration slightly decreased as increasing over-fire air rate. Meanwhile, field tests shown that the carbon content in fly ash was the lowest under the shrunk-middle-type and equal-type air distribution modes, and the super-heated steam temperature is relatively high. Moreover, the boiler efficiency under equal-type air distribution mode is significantly higher than the other three air distribution modes, about 93.39%. Therefore, it is recommended to adopt ABC mills (or BCD mills) and the equal-type air distribution mode with the over-fire air rate of 20%, which can achieve efficient and low NO_x combustion.