Thermal power unit is particularly important, for the boiler pressure affects primary frequency regulation characteristics. The existing method of generator aggregation only focuses on the generator itself, and does not consider the boiler connected to the steam turbine. In fact, the primary frequency regulation capacity of the system is positively related to the thermal storage capacity of the boiler. It is of great significance to accurately analyze minute time scale frequency response by considering the boiler model. This paper proposes a weighted method to aggregate boiler heat storage dynamics, and analyzes frequency response on the scale of minute time. The correctness of the proposed method is verified by Simulink simulation.