The invention discloses a method for predicting nitrogen oxide mission concentration of a coal-fired unit based on the neural network. The method includes preprocessing key operation parameter unit load, NOx conversion concentration and smoke temperature of SCR (selective catalytic reduction) entry, ammonia spraying flow and NOx conversion concentration of an exhaust port, establishing a BP neural network, using the unit load, the NOx conversion concentration and the smoke temperature of the SCR inlet and the ammonia spraying flow as input values, and using the NOx conversion concentration of the exhaust port as output values to obtain prediction value of the nitrogen oxide emission concentration of the coal-fired unit. By the method, workload of operators is greatly reduced, and maintenance cost is reduced.