Abstract: MgOCaO clinker was synthesized with the light burned magnesia powders and dolomite powders which produced in Liaonan. The erosion of refining ladle slag for the synthetic MgOCaO refractory was studied by means of the high temperature microscope and petrographic analysis. The results show that the synthetic MgOCaO refractory has an excellent resistance to basic slag but not good enough to acid slag. It can increase the hydrous resistance and don't decrease slag resistance when the microadditives are added to.