<p>Liquid calcium aluminate containing magnesia serves as the foundational slag for ladle slag, which is of considerable industrial importance. The effects of the MgO content and the CaO/Al₂O₃ ratio on the microstructure and transport properties of molten CaO–Al₂O₃–MgO slag were investigated using molecular dynamic simulations. In addition, the quantitative relationship between the microstructure and the transport properties of molten slag was also discussed. The results showed that Al³⁺ combines with free O²⁻ to form stable [AlO₄]⁵⁻ tetrahedral structural units. Ca²⁺ and Mg²⁺ act as network modifiers, providing charge compensation to balance the structure’s charge. While stabilizing the tetrahedra, these ions also bond with O²⁻, weakening the connections between network bodies. Increasing MgO content from 0 to 8 wt pct and CaO/Al₂O₃ ratio (R) from 0.6 to 1.2 both depolymerize the slag structure, leading to a decrease in shear viscosity and an increase in electrical conductivity. The calculated viscosity using different methods such as Einstein and Green–Kubo is consistent with the trend of experimental results. The logarithm of the electrical conductivity and the logarithm of the viscosity have a linear relationship, with a slope that aligns with previous studies.</p>