According to the fact that “The Three Norths" regional power grid contains a large proportion of thermoelectric units, and the peaking task is mainly assumed by condensing units, a peaking cost calculation method is proposed. An optimal dispatching model is built up based on the modeling of the condensing units and thermoelectric units. In this model, power load will be balanced by units in whole network, while heat load will be balanced on the spot by each thermal power plant. By solving the power outputs of all units in two different modes, the peak-regulating capacity of all units can be analyzed. Peaking cost is defined as the difference of power profit among depth peaking intervals of non thermoelectric units. The reasonableness of the calculation method is shown by an example.