In present work the 630℃ long-term aging stability of FB2 rotor steel are investigated by impact test, hardness test in combine with SEM, TEM and XRD analysis. The investigation shows that impact toughness and hardness decrease with proloning aging time. The impact ductility decreases apparently after 2000 h aging and then keeps stable. The hardness stays in a high level (253 HBW). The size and amount of M₂₃C₆ carbide increases slightly during aging without apparent coarsen. The size increase of Laves phase is more obvious and Laves phase tends to gather at grain boundary. While no chain of Laves phase is observed. The coarsen and gathering of Laves phase at grain boundary is the major reason for impact toughness degeneration. Bases on the research, it can be concluded that FB2 rotor steel keeps stable at 630℃ for up to 5000 h.