Abstract: The boiler model has become an essential parameter to evaluate the primary frequency regulation ability (PFR), and it varies with the different load in practical engineering. Based on the IEEE standard model structure, a calculation method of boiler heat storage coefficient suitable for on-line monitoring of PFR capacity is proposed. By establishing the dynamic model of flow and heat transfer, the boiler heat storage coefficient is calculated online according to the valve step simulation. Taking a 1 000 MW supercritical unit as an example, the results show that the heat storage coefficient obtained by this method can describe the dynamic changes of thermal parameters during the process of PFR more accurately. Compared with the IEEE standard model, the integrated power in 60 seconds is reduced by 62.4% using the proposed model. Heat storage coefficient changes with the working conditions. Under low load, the heat storage coefficient is large and the heat storage releases slowly. This method can identify the heat storage coefficient under the current working condition according to the on-site real-time data, and it can be applied to the on-line monitoring of PFR capacity.