Abstract: In order to solve the problems of high exhaust gas temperature,low boiler efficiency and high coal consumption of power supply units in boilers of power plants,the step utilization technology of flue gas waste heat based on the bypass flue of air preheater is adopted,which organically combines the utilization of flue gas waste heat of boilers with the regenerative extraction cycle of steam turbines.This not only dynamically optimizes the step utilization of heat energy,but also improves the performance of the air preheater.Taking a 300 MW air-cooling unit of a power plant as an example,the power supply coal consumption of the unit is reduced by 5.79g/（kW·h） after the step utilization system of flue gas waste heat is put into operation compared with that when it is not put into operation,and the thermal economy of units is significantly improved.