The residual bricks of slag line bricks after smelting low-carbon steel in the electric furnace workshop of a steel plant were selected to study the corrosion mechanism of slag line bricks by low-carbon steel by scanning tunnel electron microscope (SEM) and energy spectrometer (EDS).The results show that the carbon in the slag line brick is oxidized by FeO in the slag and O2 in the environment,and the reduction reaction of MgO and C at high temperature causes the removal of carbon and the formation of a decarburization layer,resulting in the loose structure of the slag line brick;With the formation of the decarburization layer,the slag penetrates into the decarburization layer through the loose matrix,the calcium silicate phase in the slag erodes the periclase grain boundary to form low melting point C2MS3,and the slag line brick is oxidized,decarburized and eroded repeatedly.