The invention discloses a denitration spraying ammonia automation control method which is applied to a coal-fired boiler SCR system. The method comprises the following steps of acquiring a total air volume of a boiler and an entrance nitric oxide content of the system, and multiplying the total air volume of the boiler by the entrance nitric oxide content of the system so as to obtain a total nitric oxide content in a flue gas; according to the nitric oxide content, using a predetermined basic spraying ammonia amount feedforward function to obtain a basic spraying ammonia amount; according to an entrance nitric oxide content set value of the system, acquiring a correction coefficient of the predetermined basic spraying ammonia amount, multiplying the correction coefficient by the basic spraying ammonia amount so as to obtain a target spraying ammonia amount, and taking the target spraying ammonia amount as a denitration spraying ammonia amount. By using the method, a theoretical spraying ammonia amount can match an actual-needed spraying ammonia amount; a probability of excess emission of nitric oxide and an environmental protection risk brought by the excess emission can be reduced; and negative effects and economic losses brought by excessive spraying ammonia are decreased.