With the increasingly strict pollutant emission standards, SNCR has become a new technology widely used in circulating fluid⁃ized bed (CFB) units to reduce NOx emissions. However, the difficulty of SNCR control will be increased due to the fluctuation of NOxemission concentration during variable load operation of circulating fluidized bed units. Due to the variable load dynamic NOx emis⁃sion model study is less, and in order to the realization of the dynamic prediction of NOx load change process of circulating fluidized bedunit, the article mechanism of NOx formation and SNCR reaction mechanism inside the furnace was analyzed, with coal and air volume,injection amount of ammonia, as input parameters, such as bed temperature, and mathematical modeling methods were used to establish aNOx dynamic emission model. Combined with the actual operation data of a 300 MW subcritical CFB unit, the dynamic simulation of dif⁃ferent loads was carried out. The results show that the model can better fit the NOx emission trend in the dynamic process. The average ab⁃solute errors between the calculated values of the model and the real values under 300 MW and 150 MW typical load conditions and varia⁃ble load conditions are 3.5, 1.2 and 5.7 mg/ m3, respectively, with high accuracy, which can realize the real-time prediction of NOxemission of CFB unit, with the predicted time of 4-5 min. Then, the open-loop step experiments of coal supply, air supply, urea flowand multi-variable under different working conditions were carried out. The experimental results show that the model can better reflect thedynamic characteristics of NOx emission process. The results can provide reference for the optimization of ultra-low emission control ofCFB units.