The Al2O3-SiC-C brick used in iron ladle of a steel mill was analyzed,and the erosion mechanism was studied as well. The results show that the abnormal erosion is mainly caused by MnO in the slag,and the high content of MnO makes the low-melting phase in the brick such as manganese silicate greatly increase and the molten damage generate under the scouring of high-temperature molten iron.