On the basis of equivalent enthalpy drop theory

a mathematic description

i.e. a pure heat quantity method

of heat medium going into and out from the thermodynamic system has been deduced

converting energy of the working medium used in each thermal equipment of the unit into pure heat quality coefficient ξ_j on the basis of the energy level concerning new steam quality of the unit. A mathematic model for optimizing the bled steam source distribution of deaerator has been established for thermal power plant with headerswitching system by using the said coefficient. The optimal distribution of bled steam source can be obtained by increasing or decreasing the bled steam of a certain deaerator according to the magnitude M (ξ_j) expressed by each unit. The theoretical analysis and engineering practice show that the economic efficiency of the said power plant has been remarkablely improved after optimizing distribution of bled steam source for the deaerator.