The lightweight refractory with micro-porous aggregates is of importance for energy-saving and consumption reducing in high temperature industries, and the slag corrosion resistance is significantly concerning its service life. Large industrial furnace lining is in high temperature and harsh environment, its corrosion damage is related not only to steel slag movement, but also the microstructure of materials, and hard to ascertain by experiments only. Based on Al2O3-MgO refractory for refining ladle, the lightweight microporous alumina aggregates and lightweight Al2O3-MgO refractories with excellent performance parameters have been developed, and they showed same slag resistance as the ordinary refractories in the static and dynamic corrosion experiments. Meanwhile, according to the properties of porous aggregates, a geometry model of random aggregate-matrix, in which aggregates and matrix were described with different microstructures based on porous medium theory, was adopted. And a micro-CFD (Computational Fluid Dynamics), temperature and reaction coupled model was established to describe the slag corrosion process. The characteristics of the slag corrosion on the lightweight refractories were initially investigated by mathematical simulation, and the suitable microstructure parameters and corrosion resistance mechanism of lightweight Al2O3-MgO refractories for ladle lining was discussed. The simulation results agree well with that of the experiments, which means the above model is promising for slag corrosion modeling. The key target for lightweight refractories design is the average pore size and the lightweight lining for refining ladle is feasible. It can provide a theoretical basis for design and development of lightweight refractory materials, and promote the energy-saving of high-temperature furnaces.