A steam power plant includes a first steam power plant, a second steam power plant, and an inter-unit. The first steam power plant includes a boiler, a high-pressure turbine, a first reheat line, a first feed water heater, and a high-pressure extraction steam line. The second steam power plant includes a boiler, a high-pressure turbine, a first reheat line, a first feed water heater, and a high-pressure extraction steam line. The inter-unit connected extraction steam line connects the high-pressure extraction steam line of the first steam power plant with the high-pressure extraction steam line of the second steam power plant.