The slag resistance test of MgO-CaO bricks in slag line area of AOD furnace was carried out by means of static crucible method after high temperature heat treatment at 1 700 ℃ for 3 h in air atmosphere. The corrosion mechanism of two kinds of AOD furnace slags on MgO-CaO bricks in slag area of AOD furnace was analyzed by means of XRD, SEM and EDS. The results show that the oxidation period slag with low alkalinity has obvious corrosion on MgO-CaO bricks. Under the action of surface tension and capillary force, the slag enters MgO-CaO bricks and reacts with CaO to form dicalcium ferrite (2CaO·Fe2O3, C2F) with low melting point, which promotes the dissolution of CaO and destroys the origin compact structure. The structure of reaction layer becomes loose, cracked and easy to peel off. The periclase crystal cluster in MgO-CaO bricks absorbs iron oxide, chromium oxide and manganese oxide in liquid slag and forms a composite spinel structure within and between its crystals in order to improve the viscosity of liquid slag on the surface of MgO-CaO bricks and slow down the corrosion of slag on MgO-CaO bricks. The alkalinity of reduction period slag is high and the corrosion effect on MgO-CaO bricks is weak, which is mainly manifested in the corrosion and penetration of SiO2 into the bricks, and the volume effect and temperature gradient cause the peeling of small periclase crystal cluster on the surface of MgO-CaO bricks into slag.