In order to respond to the green environmental protection spirit of the 19th National Congress of the Communist Party of China and meet the ultra-low emission requirements of circulating fluidized bed units, it is of great significance to establish an accurate NOx emission concentration mechanism control model for the design of denitrification automatic control method of circulating fluidized bed units. Based on the combustion mechanism of circulating fluidized bed boiler, the model of immediate combustion carbon was established, and the fuel nitrogen was divided into volatile nitrogen and immediate combustion carbon nitrogen to construct the self-generation model of NOx in the furnace. The NOx self-reduction model was derived by considering the reduction effect of CO and immediate combustion carbon on NOx. A selective non-catalytic reduction denitrification model was constructed, and a circulating fluidized bed nitrogen oxide emission model suitable for deep peak shaving was established based on the above models. The relationship between operating parameters and NOx emission concentration under deep peak regulation and the influencing factors of selective non-catalytic reduction denitrification efficiency were explored. The simulation verification test shows that the established circulating fluidized bed NOx model has achieved good simulation results. The average prediction time of the model calculation value under steady-state conditions is 114 s, and the average relative error with the measured value is 2.50%. The average prediction time of the model under deep peak shaving is 126 s, and the average relative error between the calculated value and the measured value is 5.42%. The calculation of the model is 2 - 3 minutes earlier than the actual measurement, which has a certain prediction effect.The designed NOx emission concentration model in this paper can provide a reference for the future research of circulating fluidized bed units to adapt to deep peak regulation, rapid load change and ultra-low emission.