The argon oxygen decarburization (AOD) furnace smelting process is widely used in the stainless-steel production. The corrosion mechanism of AOD slag to MgO-C bricks used by ladle lining was studied to provide theoretical basis for improving the service life and performance of MgO-C bricks used by ladle lining. The phase change, microstructure and chemical composition change of MgO-C bricks after corrosion were analyzed by FactSage6.2 software, X-ray diffraction (XRD), field emission scanning electron microscope (SEM) and energy dispersion spectrum (EDS). The results show that, as the corrosion reaction proceeds, periclase is gradually eroded, and the low melting point phases such as Ca3MgSi2O8 and the high melting point phases such as MgAl2O4 gradually appear. The corrosion is resulted by the penetration of AOD slag through the matrix in the MgO-C bricks, and the reaction between slag and periclase to form Ca3MgSi2O8. The generation of MgAl2O4 at the boundary of periclase hinders the corrosion of AOD slag to MgO-C bricks.