Abstract: Experimental studies were conducted on two types of micro-mixing diffusion combustors, one with a swirl number of 0.62 and another one without swirl, under the equivalence ratio from 0.3 to 0.5. The influences of swirl on the flow field distribution, flame structure, NO_x concentration, and combustion instability of micro-mixing diffusion combustion were investigated experimentally. The methods of OH^* chemiluminescence and particle image velocimetry（PIV） were used to capture flames and flow structures. Results show that adding swirl can reduce the flame height by 44% and shorten the residence time by changing the flow field structure, ultimately achieving a 63.4% reduction in NO_x emissions. Without swirl, the main driving factor of micro-mixed diffusion flame pulsation is the formation of radial expansion zone under high equivalent ratios, while swirling flow can inhibit the formation of radial expansion zone, so as to achieve the effect of suppressing combustion oscillation in a wide load range.