The invention discloses oxide dispersion strengthening low activity ferrite/martensite steel and a smelting technology and a smelting method of the oxide dispersion strengthening low activity ferrite/martensite steel, and belongs to the technical field of special steel metallurgy. The oxide dispersion strengthening low activity ferrite/martensite steel comprises raw materials including, by mass percent, 8.9%-9.1% of electrolytic chromium, 0.4%-0.5% of electrolytic manganese, 0.05%-0.08% of high-purity silicon, 0.08%-0.12% of high-purity graphite, 1.4%-1.6% of metal tungsten, 0.1% of metal tantalum, 0.18%-0.22% of metal vanadium, 0.1%-0.25% of sponge titanium, 0.2%-0.5% of high-purity rare earth yttrium, 1% of oxide scales and the balance high-purity low-sulfur low-phosphorus pig iron. A preparing method of the oxide dispersion strengthening low activity ferrite/martensite steel comprises material preparing, vacuum induction smelting, casting, forging and electroslag remelting processes, ODS-RAFM is prepared, and the large-specification ODS steel high in density, uniform in component, little in energy consumption, high in purity, stable in smelting method and capable of meeting the need of large nuclear power equipment is achieved.