Abstract: Ammonia-coal cofiring is one of the most promising technology routes to reduce CO₂ emissions from coal-fired power plants. Since ammonia differs significantly from pulverized coal in terms of its heating value, combustion characteristics, flue gas composition and radiation characteristics, ammonia-coal cofiring may strongly affect the heat transfer distribution and steam parameters of coal-fired boilers which may become one of the key problems restricting the application of ammonia cofiring in coal-fired power plants. To investigate the effects of ammonia cofiring on the radiation heat transfer of boilers, a three-dimensional （3D） CFD numerical model suitable for ammonia-coal cofiring is constructed and employed to investigate the flow, temperature and heat transfer distributions of boiler under ammonia cofiring conditions. Because the concentrations of CO₂ and H₂O in flue gas will vary over a wide range with the change of ammonia cofiring ratio that far exceeds the application range of the Smith weighted-sum-of-gray-gases （WSGG） model commonly used in the calculation of gas absorption coefficient in coal combustion CFD models. Thus, the Johansson WSGG model that is applicable to a broader range of flue gas compositions is incorporated into the CFD model such that the model is suitable for the simulation of radiation heat transfer in ammonia-coal cofiring boilers. Based on that, the flow, temperature and radiation heat transfer characteristics of ammonia cofiring in a 600 MW boiler are numerically studied and compared with those of coal combustion case. The results indicate that using the Smith WSGG model to calculate the gas absorption coefficient is going to significantly overestimate the heat transfer of furnace waterwall under high ammonia cofiring ratios. In addition, it is found that because the air and flue gas mass flow rates of ammonia-coal cofiring and coal combustion cases are very close under the same total thermal input, their flow and temperature distributions in the furnace are also very close. Therefore, under lower ammonia cofiring ratios （less than 20%）, ammonia cofiring will not significantly affect the heat transfer of furnace waterwall.