There exist certain limitations to research the law and influence factors of the nitrogen oxides formation only with the help of field tests, because the nitrogen oxides formation of the boiler is influenced by various factors. The flow, combustion mathematical models interrelated and so on are established taking the 410t/h boiler fired tangentially as a prototype by the use of the fluent software. All the mathematical models are verified and modified with the aid of routine field test data, and the accuracy and reliability of the mathematical models are improved. Then NOx formation performance is stimulated in allusion to the influence factors without field test conditions. The mathematical simulation results show that mathematical models can provide a sufficient theoretical basis to analyze accurately combustion and NOx formation law in furnace, and the deficiencies of field tests have been made up.