Liquid lead and lead-bismuth eutectic (LBE) are considered primary candidate materials for coolant in advanced lead fast reactors, and also, for coolant and spallation target in accelerator-driven systems because of their favorable thermal-physical and chemical properties. However, liquid lead and LBE exhibit substantial structural material corrosion, which is considered one of the critical challenges in the liquid lead or LBE application. Among the effective methods to reduce the corrosive effect, careful control of the oxygen content dissolved in the liquid introduces a protective oxide layer on the surface of the structural material. Ferritic-martensitic steels with (9%-12%)Cr (mass fraction) have been considered promising structural materials in the advanced lead fast reactor and accelerator-driven system. Oxide scale with duplex structure is formed on the (9%-12%)Cr ferritic-martensitic steels in oxygen-containing LBE, but the oxide scale grows rapidly enough to cause the substrate recession. Recently, pre-oxidation treatment was proposed to further improve the corrosion performance in LBE. As reported, grain refinement promoted the formation of oxide scale without chemical modification. However, grain refinement effects on the oxide scale formation of (9%-12%)Cr ferritic-martensitic steels are not clear, and the effect of oxide scale through pre-oxidation treatment on the corrosion performance in LBE is rarely reported. In this study, the oxide scale formation behavior during pre-oxidation in air at 650^oC on the 9Cr2WVTa ferritic-martensitic steel after different cold rotary-swaging deformation rates was analyzed using SEM, XRD, EPMA, and XPS, and the effect of pre-oxide scale on the corrosion performance in stagnant oxygen-saturated LBE was further investigated. The results demonstrated that the high-temperature oxidation resistance in air was enhanced by increasing the diameter reduction. A slight improvement in oxidation resistance was observed after 63% deformation, while significant enhancement in oxidation resistance was present in ultrafine-grained sample fabricated by 94% deformation. The oxide particle size was slightly reduced in the sample produced after 63% deformation during air oxidation compared with the tempered sample, but (Fe, Cr)₂O₃ oxide particles were formed on both samples. The size of oxide particles was significantly reduced and Mn-riched oxide (MnCr₂O₄ and Mn₂O₃) was promoted in the ultrafine-grained sample. The presence of Mn-riched oxide with good stability improved the oxide scale compactness. The compact oxide scale on the ultrafine-grained sample using pre-oxidation treatment at 650^oC for 20 h effectively suppressed the corrosive attack of LBE and the outward diffusion of Fe through the pre-oxide scale after exposure for 500 h to stagnant oxygen-saturated LBE at 550^oC. The higher solubility of Mn in LBE promoted the dissolution of the Mn-riched pre-oxide scale. The gradual dissolution of Mn in pre-oxide scale and corrosive attack by LBE led to the breakdown of the pre-oxide scale, which was supported by the formation of a continuous corrosion product layer after exposure for 2000 h to stagnant oxygen-saturated LBE.