The invention discloses a method for outputting effective output efficiency of a boiler. The method comprises the following steps of: determining real-time air dry base ash content of equivalent fuel in the boiler through air dry base ash content of the equivalent fuel and fire coal consumption of the equivalent fuel, further establishing a function relationship between the received base lower heating value and the air dry base ash content, and further calculating the real-time efficiency of the boiler. The method for acquiring the effective output efficiency of the boiler is provided, online measurement of elemental analysis of charged coal and online measurement of ash combustible content are avoided, and according to the method, the operation is easy and the accuracy is high; and therefore, the method for calculating the efficiency of the boiler is simplified.