A combined heat recovery device includes a high pressure cylinder of a steam turbine; a main steam pipe; a final-stage steam extraction pipe; an additional pipe additionally provided on the main steam pipe; a heat exchanger taking main steam in the main steam pipe as a heat source; a feedwater heater taking discharged steam from the heat exchanger as a heat source; and a steam side regulating valve provided on the additional pipe, configured to regulate main steam in the additional pipe, and capable of controlling a pressure of extracted steam behind the steam side regulating valve to control an outlet temperature of the feedwater heater to reach a preset feedwater temperature.