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Coal-fired power plants remain a significant source of CO 2 emission, NH 3 /coal co-firing in existing coal-fired boilers can rapidly and effectively reduce CO 2 emissions. However, the unique physicochemical properties of NH 3 result in unstable combustion and high NO x emissions. Superfine pulverized coal combustion and moderate or intense low-oxygen dilution (MILD) combustion are two advanced technologies with stable combustion and low NO x emissions. This study systematically investigated the coupling of these two technologies in NH 3 /coal co-combustion. Results show that the synergistic effect of superfine pulverized coal and MILD combustion ensures stable NH 3 /coal flame propagation, with a shorter lift-off distance and a higher peak temperature (70 K–100 K increase) under higher NH 3 blending ratio (NBR) conditions. As the NBR increases from 0 to 40 cal%, the maximum Da s-O2 for the superfine particles (18 μm) decreases from 0.55 to 0.49, while for normal particles (125 μm), it decreases from 3.9 to 3.4. The combustion state of superfine particles more easily approaches the MILD combustion state. The value of R char-H2O /R char-CO2 increases from 0.64 to 1.93, indicating the C Char -H 2 O reaction dominates the char gasification behavior. Compared to that for normal particles, the NO emission concentrations for superfine particles combustion at 0, 10 cal% and 20 cal% NBR were reduced by 48 %, 64 % and 47 %, respectively. These findings provide new insights and theoretical guidance for stable combustion and low NO x emissions of NH 3 /coal co-firing. [Display omitted] • Coupling MILD with superfine particle combustion in NH 3 /coal co-firing is proposed. • The combustion state of the superfine particle is closer to the MILD regime. • C Char -H 2 O reaction dominates the char gasification behaviors at high NBRs. • The NO emission of superfine particles are lower than those for normal particles. [ABSTRACT FROM AUTHOR]