Precise control of ammonia injection is an important technology in selective catalytic reduction(SCR) denitrification system in power stations. Inaccurate control will reduce the denitrification efficiency or cause secondary pollution of ammonia and even block the air preheater. Establishing an accurate dynamic model for the SCR denitraiton system is the basis for development of advanced ammonia controllers. By analyzing the difference between the reaction characteristics of the SCR denitration catalyst with flue gas in power plants and those in laboratory

classical kinetic equations of the SCR denitrification were improved. The dynamic mechanism model of the SCR denitrification in coal-fired power stations was established and compared with the model based on classic kinetic equations. Finally

the characteristics of the improved model under unstable conditions with the inlet NO_x concentration and the flue gas flow rate fluctuate greatly are analyzed. The results show that

this improved model has better accuracy and adaptability under both stable and unstable operating conditions.