Abstract: The enhancement of thermal power unit peak shifting and frequency regulation capability is an important method to build a new power system. In this manuscript, from the perspective of boiler-turbine energy flows decoupling, a phase-change energy storage system through extracting the part medium-pressure cylinder exhaust steam for storing energy is designed and coupled with a thermal power unit; the control strategy through reconfiguring load commands of turbine-boiler-storage three systems is proposed for the above integrated system. Then a case study of a 660 MW (Pe₀=660 MW) ultra-supercritical unit is analyzed. Erythritol with the melting temperature of 117.7 ℃ is selected as the energy storage material based on the exhaust steam parameters of the medium pressure cylinder. Then, the influence of exhaust steam ratios on load reduction performance of the integrated system is studied. The result shows that the equivalent load down rate of the unit can be increased from 2.00% Pe₀/min to 5.13% Pe₀/min when the steam extraction ratio changes from 0.00 to 0.85; the maximum heat storage capacity of the energy storage system is 118.73 GJ, and the maximum of exergy storage capacity is 28.97 GJ. After the load command reconfiguration, the thermal efficiency of the integrated system during transient processes increases by up to 1.85%, and the exergy efficiency decreases by a maximum of 2.23%.