The invention relates to an intelligent ammonia injection control system suitable for full load. The system includes a flue gas denitration device CFD flow field and gas-solid two-phase mass transfer reaction based coupling model part and a predictive control based flue gas denitration device ammonia injection amount calculation part. A flue gas load is divided into multiple subintervals, CFD is utilized to construct a CFD flow field model library of an SCR (selective catalytic reduction) device under different loads; a CFD flow field model matching a current load is selected from the flow field library, and according to the flue gas loads of different subintervals, the opening degree of ammonia injection branch pipes in all subintervals can be adjusted in real time; and an MIMO nonlinear model identification method is utilized for ammonia injection system model identification, a predictive control module is added to a feedback loop, rolling optimization and online correction characteristics of predictive control are utilized to ensure stable operation of the system and performance reaching the standards. The system provided by the invention combines database, divisional control and intelligent control technologies, and can effectively reach the purposes of reducing energy consumption, lowering cost, increasing economic benefits and the like under full load of coal-fired flue gas.