Abstract: Based on the operation characteristics of axial-flow fans regulated by dynamic and static blades widely used in large thermal power units, a mathematical model of fan operation performance is established. The calculation expressions of fan flow, total pressure and specific power are established in the model. The flow and total pressure of the fan are calculated based on the field operation data, and the calculation results are modified by using the parameters of atmospheric conditions and density and air leakage rate. The flow, total pressure and specific power calculated in the model are fitted with the actual performance curve of the fan, and the operating conditions of the fan are obtained. The fan operation efficiency is calculated by the fan efficiency curve. Compared with the strict performance test of the fan, it is shown that the model has better computational accuracy and universality in the characterization of the fan performance. The model can use the real-time data to monitor the fan efficiency and the historical data to analysis the fan efficiency retrospectively. When the unit carries out the renovation project involving the change of gas and air system, the model can be used to calculate the operation efficiency and fan margin of the modified fan, which can accurately predict the operation state of the modified fan and provide theoretical support for the renovation project.