Abstract: One of 350 MW supercritical thermal power unit has significantly reduced its primary frequency regulation ability after undergoing high and low bypass heating renovation. Under deep peak shaving conditions, the load variation cannot meet the requirement of 75% when the frequency regulation action is taken for 15 seconds. Through a comprehensive analysis of factors that affect frequency regulation, such as changes in flow rate of the high-pressure regulating valve of the steam turbine, frequency regulation control circuit, and main control circuit of the steam turbine, it is concluded that insufficient heat storage in the boiler caused by high-pressure bypass heating diversion is the main reason for the decrease in frequency regulation capacity. In order to improve the heat storage of boilers under low loads,on the one hand, a new energy demand model on both sides of the turbine and boiler is established using the direct energy balance law to achieve continuous supplementation of high bypass steam for heating. At the same time, the feed forward loop of the frequency control valve position and the main control of the turbine are enhanced to improve the fast response of the frequency control load; On the other hand, an override control circuit for the heating high bypass control valve was designed to achieve energy storage assisted frequency regulation, which means that after the frequency regulation action, the heating high bypass is controlled to override according to the direction and amplitude of the action.Through the above optimization, the unit successfully completed a frequency regulation test at 25% rated load.