•Ce made the shape of magnetite island change from roughly circular to slat-like.•The magnetite pellets of both CLAM and Ce-CLAM specimens had a growth trend from small to large.•Ce enhanced the adhesion, continuity and integrity of oxide scale, and delayed the evolution of magnetite.•The mechanism model of Ce effect on the evolution of magnetite and the scale growth model of the two kinds of specimens were proposed. Lead-cooled fast reactor (LFR) is one of the six types of fourth-generation advanced nuclear reactors, and the corrosion with liquid lead-bismuth eutectic (LBE) to structural materials is regarded as a major obstacle restricting the development of LFR. This study focused on the surface morphology of oxide scale, aiming to illustrate the evolution law of oxide scale and the mechanism of Ce effect on oxide scale. China low activation martensitic (CLAM) and Ce-containing CLAM (Ce-CLAM) specimens generated roughly circular and slat-like magnetite islands respectively, but their magnetite pellets had similar growth trends from small to large sizes. Ce delayed the evolution of magnetite, enhanced the adhesion, continuity and integrity of oxide scale for Ce-CLAM specimen. The mechanism model of Ce effect on the evolution of magnetite and the scale growth model of the two kinds of specimens were proposed.