The invention discloses a flame-retardant steel-aluminum composite plate core material, and relates to the technical field of composite material preparation and processing. The composite plate core material is composed of a steel plate and two aluminum alloy plates, the steel plate is located between the aluminum alloy plates, and the composite plate core material is prepared by a rolling technology. The preparation method comprises the following steps: preprocessing, rolling and annealing treatments of the steel plate and the aluminum alloy plates. The steel plate and the aluminum alloy plates are rolled through a two-pass rolling process, and relevant process parameters are strictly controlled, so the steel plate and the aluminum alloy plates have a high bonding strength, are not prone to be separated, and achieve excellent mechanical properties; and vibration treatment is set in the rolling process, so a static pressure is applied to above materials in the rolling process, a deformation area is also vibrated, and the deformation resistance of the material is reduced, thereby the rolling capability is improved.