The article presents the optimization method of load division between combined heat and power plant units. The method used the power unit division into functioning parts and the differentialexergy method. This method allowed presenting the unit as a structural diagram where exergetic subsystems are fuel supply, steam generator, turbine, generator and electrical equipment, water supply and regeneration, heat supply to the consumer. The differential-exergy method was based on a combination of exergy analysis and optimization method of economic efficiency criteria using uncertain Lagrange multipliers. The use of the exergy function of goal allowed avoiding the problem of division of fuel costs for each type of product that was important at optimization. The optimization criterion, its parameters and limitations were developed as well. These parameters can extend traditional technical and economic analysis of the combined heat and power plants operating mode, as they take into account thermodynamically rigorous division of fuel costs between heat and electric power at their complex production on the combined heat and power plants. The use of the differentialexergy method in optimizing the load distribution of the power units of the combined heat and power plants makes possible obtaining of fuel savings of 1.5 to 3%. It has been shown that if the parameters of power units deteriorate, the application of the method makes it possible to have the best performance of the power plant when it is compared with functioning of combined heat and power units at proportional loading.