Abstract: The increasingly strict emission standards on NO_x put forward higher requirements for the performances of the coal-fired industrial boilers. It is hard for the existing burners in industrial boilers to meet the emission restrictions by operation optimization. In this study,a new type of coal-fired low-NO_x swirling burner for industry boilers was developed. Through the experiments in a 25 t/h industry boiler,the effects of primary air ratio,secondary air distribution,swirling angle,recirculated flue gas( FGR) and over fire air( OFA) ratio on NO_x emission and combustion efficiency were studied. The results show that the NO_x emission increases when the primary air ratio increases from 7.8% to 8.5% and the inner/outer secondary air ratio increases from 0.67 to 1.32. As the angel of swirl vane increases from 30° to 60°,the NO_x emission decreases first and then increases. With the increase of FGR ratio from zero to 13.3%,the NO_x emission first decreases and then tends to be stable. The effect from OFA ratio on NO_x emission is slight,and with the increase of OFA ratio,the NO_x emission first decreases,and then increases. During the test process,the coal stream flame is stable and the unburned carbon content in fly ash( UBC) is always lower than 25%. The lowest NO_x emission is obtained as 171-178 mg/m~3( 9% O_2),with a UBC value of 14.9% and a boiler efficiency of 91.7%.