Abstract: Ammonia (NH3), a promising zero-carbon fuel, faces challenges of combustion instability and high NOx emissions. Blending NH3 with highly reactive coke oven gas for combustion enhances the reactivity of NH3, facilitating carbon emission reduction in the steel industry. Flameless combustion is effective in suppressing NOx formation; however, there are few systematic studies on nitrogenous pollutant emissions (NO, N2O and HCN) during the flameless combustion of NH3/coke oven gas fuels. For the combustion process of ammonia fuel, the fuel can be used as a reducing agent for NOx. NOx emissions are controlled by both NOx formation mechanisms and selective non-catalytic reduction (SNCR) mechanisms. In this paper, the effects of the air nozzle dimension, equivalence ratio (Φ), SNCR nozzle position, and the NH3 reductant flow rate (QNH3) on nitrogenous pollutant emissions (NO, N?O, and HCN) and NH3 escape during flameless combustion of NH?/coke oven gas are investigated using computational fluid dynamics (CFD) simulations in a 3 MW heating furnace. The numerical simulation method has been experimentally validated. The key structure optimization of the NH3/coke oven gas flameless burner has been completed. The results indicate that compared to conventional flame combustion, flameless combustion of NH3/coke oven gas reduces nitrogenous pollutant emissions by approximately 75%. Further integration with SNCR technology can reduce nitrogenous pollutant emissions by approximately 84%. For NH3/coke oven gas, NO is the primary nitrogenous pollutant, with NO2 concentrations consistently below 3 ppm. With increasing equivalence ratio (0.7–1), NO concentration decreased from 1483 ppm to 172 ppm. N2O first decreases and then increases, reaching a minimum of 29 ppm at the equivalence ratio of 0.9. When the equivalence ratio is 0.9, both NO and N2O concentrations first decrease and then increase with increasing air jet velocity. The emission of nitrogenous pollutants reaches its minimum at the air velocity of 72 m/s. For ammonia combustion with SNCR technology, the SNCR nozzle should be positioned downstream of the nitrogenous pollutant formation zone, appropriately distant from the peak NO generation area, with the temperature range of 1200–1400 K. With increasing QNH3, NO concentration first increases then decreases, while N2O concentration and NH3 escape monotonically increase. This study investigates the deep nitrogen reduction characteristics of NH?/coke oven gas flameless combustion coupled with SNCR technology, providing theoretical support for the clean and efficient combustion utilization of ammonia fuel in industrial heating furnaces.