The invention relates to the field of energy saving and consumption reducing, in particular to a device for reducing the back pressure of a steam turbine through waste heat of exhaust smoke of a boiler. The device comprises a waste smoke waste heat recovery unit, the steam turbine, a deaerator, a condensing engine, a heat pipe and a heating unit. The waste smoke waste heat recovery unit is connected with a superheater, a sectioning valve is arranged between the superheater and the steam turbine, the steam turbine is connected with an electric generator, and the condensing engine is arranged below the steam turbine. The deaerator is connected with an air pump and connected with a condensate water pump, a water feeding pump is arranged on the left side of the deaerator, and the superheater is arranged above the water feeding pump. The waste smoke waste heat recovery unit is composed of an exhaust port, fans and a filtering net, and the fans are arranged at the upper end and the lower endof the waste smoke waste heat recovery unit. The device can save energy, increase the utilization rate of energy, greatly reduce the index of pollution of waste smoke to air and be good for the environment and the health of people, the working loss of the device is reduced, and the service life is prolonged.