Abstract: To meet the “peak carbon and carbon neutrality” targets, the gradual reduction of coal-fired electricity generation through the co-firing of coal and NH₃ has emerged as a new pathway to achieve carbon reduction. However, the co-firing characteristics of coal and NH₃ are not yet clear. Therefore, the coal/NH₃ co-firing experiments were conducted based on a flat-flame burner to investigate the influence of ammonia blending ratio (E(NH₃), 0−100%) and coal/NH₃ injection methods (pre-mixed, non-pre-mixed) on combustion characteristics. Camera, flue gas analyzer, and thermocouples were used to observe flame morphology, gas composition, temperature distribution along the centerline heights above the burner (H_AB), and measure the unburned carbon content in fly ash. The results showed that during the initial stage of combustion, the competition for O₂ between coal and NH₃ was more pronounced. The NH₃ combustion in the combustion zone created a rich water vapor atmosphere. Under low E(NH₃) conditions in pre-mixed combustion, CO reacted with OH, resulting in a decrease in CO concentration. On the other hand, under high E(NH₃) conditions, NH₃ preferentially reacted with O₂, leading to an incomplete combustion of a significant amount of carbon. Additionally, the rich water vapor atmosphere promoted coal gasification reactions, resulting in a significant increase in CO concentration in the combustion reduction zone, reaching a maximum of 19773.05 mg/Nm³. However, this process altered the pore structure of the coke, increased the specific surface area of the coke, accelerated the combustion process of coal powder, and reduced the residual carbon content in fly ash from 13.90% (pure coal combustion) to 13.44% (E(NH₃)=80%) under pre-mixed conditions. An early injection of NH₃ reduced the preheating effect of NH₃ combustion on coal powder and decreased the combustion intensity in the flame reaction zone. The addition of NH₃ significantly increased the NO_x emissions, and with increasing E(NH₃), there was an initial increase followed by a decrease in NO_x, with the peak concentration of NO occurring earlier. The unburned NH₃ content and oxygen content were the main factors influencing the formation of N₂O and NO₂. Increasing the residence time of coal/NH₃ combustion, reducing the unburned NH₃ content, and creating a reducing atmosphere were effective ways to reduce NO_x emissions. Under high E(NH₃) conditions in pre-mixed combustion (E(NH₃)≥80%, H_AB=100 mm) and non-pre-mixed conditions, the CO₂ percentage showed a decreasing trend with increasing E(NH₃). Pre-mixed conditions with an E(NH₃) range of 40% to 60% were more favorable for achieving low nitrogen, low carbon, and high-efficiency combustion of coal/NH₃. The co-firing of coal powder with NH₃ exhibited mutual promotion and restriction effects, requiring some effective measures based on specific circumstances to harness the promotion effect of coal/NH₃ co-firing.