In order to solve the problem that the traditional denitration method, selective non-catalytic reduction (SNCR), causes the temperature of the boiler area to drop sharply, and serious ammonia escape and affects the combustion efficiency and denitration efficiency, in small coal-fired boilers, high molecular amino material with 1,3,5-triazine as the main raw material is used as denitration agent to replace the ammonia water or urea solution in the traditional SNCR denitration process, so as to change wet denitration to dry denitration. The dry denitration uses the denitrification powder to be sprayed into the combustion zone of the boiler furnace to react directly with nitrogen oxides to produce N2 and water. Through the application of the method in the denitration renovation project of a coal mine boiler room, it not only does not affect the combustion condition of the boiler, but also increases the efficiency of the denitration from the original 50% to 75%, and the cost is reduced by 3/5.