Abstract: According to the characteristics of reheat section extraction steam heating mode, a method of thermal economy calculation was presented. Taking domestic thermal power units as the research examples, comparisons and analyses were conducted on the thermal economy of extraction steam heating mode through cold reheat section and hot reheat section based on different unit loads and different unit capacities. Calculation results show that, under the same heating steam flow rate, the thermal economy of the unit increases with the decrease of the unit load, and the energy saving advantage of the extraction steam heating mode through cold reheat section dwindles compared with through hot reheat section. Additionally, the thermal economy of the small capacity unit is better than that of the large capacity unit under heating condition.