Denitration system adopting staged combustion and process

The invention discloses a denitration system adopting staged combustion and a process, and belongs to the technical field of cement production. The denitration system comprises a smoke chamber and a decomposing furnace, the decomposing furnace communicates with a tertiary air pipe, a discharging assembly and a backflow assembly, and the discharging assembly comprises a pulverized coal injection pipe, a discharging pipe, a furnace inlet pipeline I and a furnace inlet pipeline II. The decomposing furnace in the staged combustion mode is adopted, the air inlet amount of the tertiary air pipe is adjusted, meanwhile, under the effect of enlarging a reduction area of the decomposing furnace, the staying time of gas in the reduction area is prolonged, under the support of introducing secondary fuel into the decomposing furnace through the furnace inlet pipeline I and the second furnace inlet pipeline II, nitrogen oxide generation amount control in the production process is achieved, the ultralow emission requirement