The in-depth energy conservation of thermal power units is confronting new challenges under the varying operation conditions and ambient constraints. The description of energy-consumption benchmark state was proposed to describe the economic performance of thermal power units with the varying operation boundary, operation conditions and equipment performance. Based on the fuel specific consumption analysis theory, the energy consumption interactions of units were divided into 4 parts: parameters, equipment, subsystems and units. The models for energy-consumption benchmark states were established with the fuel specific consumption setting as the optimization objective. Such a method was performed on a 600 MW supercritical power unit and the results show that the energy-consumption benchmark state, which is related with the varying boundary, can reflect the boundary condition, operation lever and equipment performance. It makes significant reference for the energy-saving diagnosis and operation optimization of thermal power units under overall working conditions. © 2015, Science Press. All right reserved.