The invention discloses an optimum scheme of an ultra-supercritical secondary reheating unit, and refers to a secondary reheating unit of a coal-fired power plant after optimization of a back heating system, parameter optimization of main steam, primary reheating steam, and secondary reheating steam, and structural optimization of a turbine body. The optimum scheme of the ultra-supercritical secondary reheating unit can obviously reduce the heat loss of the secondary reheating unit, and significantly decrease greenhouse gas emission and decreases cost of the ultra-supercritical secondary reheating unit obviously. By taking a 1200 MW grade unit as an example, four mono-axial cylinders are used for gas exhausting, the ultra-supercritical secondary reheating unit is composed of a single-flow ultra-high pressure cylinder capable of completely supplying water, back-heating and pumping gas, a dual-flow high and medium pressure cylinder, and two dual-flow middle and low pressure cylinders; there is no middle pressure cylinder and a middle low pressure linking pipe; no gas pumping opening is arranged on the high middle pressure cylinder and the middle low pressure cylinder; the water supply and back heating are provided by a first pump, a new second pump, a new third pump, and a new fourth pump; a ultra-low temperature coal economizer, and a heat primary wind condensing water heater replace a seventh pump, an eighth pump, a ninth pump, and a tenth pump to heat the condensed water; all low-pressure heaters are canceled.