Abstract: The current environmental policy requires that the NO_x emission of power station boilers is qualified by the control hourly average, while the real time value of emissions is not required. In order to further reduce NO_x emissions from power station boilers, improve operation stability and maximize the potential of SCR system, the study and optimization of the influence factors on NO_x generation and removal of power station boilers was carried out. Thereby the real time values of NO_x emission were all up to standard, and the boiler efficiency improved. The phenomenon of short-term over standard was avoided in the changing condition of the boiler load adjustment. It achieved good results in the safety, stability and economy of the system, and greatly reduced the workload of daily operation adjustment.