Abstract: Based on the operating data and the current state of the unit to determine the best exergy efficiency that the thermal power unit can achieve, is a practicable target to guide the field operation and achieve energy saving and emission reduction. This paper analyzed the exergy efficiencies gap between the actual working conditions and the design working conditions and then put forward the idea of separating the influence factors that decay the efficiency into equipment performance degradation and personnel operation. Based on the actual operating data of the unit and the data mining method, the exergy efficiency prediction model was established with the control index parameters as inputs. Taking a 330 MW CFB unit as an example, the exergy efficiency prediction model training and verification was carried out. Finally, based on stochastic simulation analysis, the actual optimum exergy efficiency with its optimal control index parameters were obtained under various load conditions. The method proposed in this paper could provide field operators quantitative guidance for optimal operation and control of coal-fired power plants.