Abstract: Taking a 600 MW coal-fired unit as the research object,in order to adapt to the deep flexible peak shaving of the unit,the flexibility transformation research of steam pump recirculation system is carried out. The internal leakage of steam pump recirculation valve under deep peak shaving operation is serious,which affects the operation safety of water supply system and causes the loss of steam pump energy consumption. It analyzes the causes of serious internal leakage of recirculation valve,and analyzes and compares the transformation technical measures such as refitting pneumatic isolation valve,optimizing control logic and installing small bypass of steam pump recirculation from the aspects of technical safety,reliability and economy. According to the operation background of the power plant and the operation characteristics of the valve,it is determined that the installation of steam pump recirculation small bypass is the best transformation scheme,which provides a reference for the same type of units.