The invention relates to a soft measurement based ammonia injection grid partition control method. An ammonia injection grid changes all original manually adjusting doors to pneumatic (or electric) control valve. The control method includes the steps of 1), acquiring and pre-processing data, wherein the data acquisition comprises the measurement of NOX and O2 at an inlet of an SCR (Selective Catalytic Reduction) reactor as well as NOX, O2 and ammonia escape rate at an outlet of an SCR reactor; 2), establishing soft measurement models according to the acquired data; 3), combining the plurality of static soft measurement models with disturbance quantity unit load and coal mill combination to generate a dynamic controller for controlling the opening size of every pneumatic control valve of the ammonia injection grid for further controlling the amount of ammonia injection of every adjustment door, thereby achieving ammonia injection in equimolar ratio of the ammonia injection grid partition. Compared with the prior art, the soft measurement based ammonia injection grid partition controlling method has the advantages of improving the denitration efficiency, reducing the ammonia escape rate and investment and operating costs and the like.