Abstract: The superheat degree of steam extraction is high in the ultra-supercritical single reheat unit. It results in largely irreversible loss and poor system perfection. The thermodynamic performance of the MAST CYCLE thermodynamic system was analyzed, which can effectively reduce the superheat of regenerative extraction steam. However, the system is relatively complex. The optimization system of single reheat with 4-stage external coolers is the best scheme of system integration, and the power supply efficiency reaches 49.58%. The waste heat of the system was used. The calculation results show that the power supply efficiency of the system reaches 50.07%, which provides a more effective way for the optimization design of 700℃ ultra-supercritical unit system.