The invention relates to an additive for a high-performance Al2O3-SiC-C castable and a preparation method of the additive. The additive comprises the following components in parts by weight: 5-9 partsof iron-aluminum spinel, 1-3 parts of carbon black, 1-3 parts of silica micro powder, 3-6 parts of alumina micro powder, 2-4 parts of zirconium dioxide, 1-3 parts of silicon-iron nitride and 1-2 parts of magnesite. When the additive provided by the invention is added into the Al2O3-SiC-C castable, the castable has good structural flexibility, the brittleness of the castable is effectively reduced, and the peeling resistance is improved; infiltration of molten iron is effectively resisted and the erosion is reduced; SiC and mullite which are formed in situ can form a network structure, so thatthe bonding strength is improved and the matrix is strengthened; with the addition and in-situ formation of a nitride, the erosion resistance and the impact resistance are improved; and with the introduction of the additive, the structural toughness, the peeling resistance, the abrasion resistance and the slag-iron erosion resistance of the castable are improved, and the service life of the Al2O3-SiC-C castable is prolonged.