This research paper investigates the effects of boiler swing and firing rate of power plant boilers on NO emissions. For this purpose, a nonlinear state space dynamic model has been developed on the basis of collected field experimental data to relate the NO emissions of drum boilers with other state variables. The collected experimental field data were used to determine the model coefficients. The NO formation computations were conducted using a Matlab program, and model response was validated with experimental data obtained from the literature. The current model results are in good agreement with the experimental data from the literature. The NO formation was obtained as a result of four steam flow rate perturbation schemes: (i) eight steps of 5%/min, (ii) four steps of 10%/min, (iii) two steps of 20%/min, and (iv) one step of 40%/min. The research results reflect that the total NO formation over a period of time decay with lower swing rates and the magnitude of the total formed NO over a period of time increase as the swing rate increases. The model was then implemented to predict the NO emission variations from boiler field data.