Abstract: It is required by the "dual carbon" policy that the operation of power plant boilers shall develop in a more stable and efficient direction, while the thermal efficiency of boilers is an important indicator to measure the level of boiler operation. The commonly used direct and indirect balance calculation methods, as well as some soft measurement model calculations, have poor representativeness and timeliness in obtaining boiler efficiency due to the delay of coal quality test, and cannot provide accurate and effective boiler adjustment reference. Combining the direct and indirect balance calculation methods for boiler efficiency, a dynamic update method based on the iteration of the quality of the boiler's incoming coal can improve the accuracy and timeliness of the real-time calculation results of boiler efficiency. Through comparison and verification of different boiler efficiency calculation methods, the real-time calculation results of boiler efficiency based on the dynamic update iteration of the coal quality are closer to the test results of on-site boiler efficiency, compared to the ordinary real-time calculation results of boiler efficiency.