Abstract: NOx emission of coal-fired thermal power units is an important environmental protection and safety index. Due to the pure time-delay characteristics of NOx controlled objects, conventional PID control is difficult to control the NOx index of flue gas denitrification to an ideal range. In this paper, a new denitration control strategy for thermal power units based on γ incremental Stair-like generalized predictive control was introduced. The new control strategy was applied in a 600 MW coal-fired thermal power unit. The result shows that the NOx emission was obviously reduced. The control quality is effectively improved.