Abstract: To reduce heating energy consumption, using heat pumps to recover waste heat from flue gas can effectively improve the heating efficiency of the unit. Taking a 300 MW subcritical CFB boiler unit as an example,a low temperature economizers and a flue gas condensers are set before and after the desulfurization tower to form a new heat pump heating system, a thermodynamic model for this heat pump recovery of flue gas waste heat was established to analyze the impact of flue gas waste heat utilization methods on the thermodynamics and heating performance of the heat pump. The results show that,a low-temperature economizers is arranged, under the design conditions, when the coefficient of performance(C_OP) of the heat pump is 1. 746, the flue gas temperature decreases from 130 ℃ to 90 ℃,which could as a high-temperature heat source of the heat pump, 20. 87 MW of waste heat can be recovered at most, and the water consumption of the desulfurization tower is reduced by 28. 792 t/h; A flue gas condenser is arranged, which can be used as a low-temperature heat source for the heat pump. At the same time, 10. 10 MW waste heat can be recovered, and 13. 654 t/h condensed water can be recovered. When the return water temperature of the heating network increases, C_OP decreases, but the efficiency of the heat pump system and the heating system increases. When the water temperature at the condenser outlet increases, the C_OP and heating system efficiency decreases, but the efficiency of heat pump system increases. It is shown that, the heat pump heating method of recovering waste heat from flue gas can effectively utilize the lower order energy of flue gas and has good energy-saving and water-saving benefits.