<p>To meet the development requirements of low-reactivity mold fluxes for high-aluminum steel continuous casting, the topological order of molten slag and its regulatory mechanism on thermophysical properties are crucial. The present work uses molecular dynamics (MD) simulations to elucidate the effects of alkali metal oxides Na₂O and K₂O on the oxygen network structure, viscosity, and thermal conductivity of calcium aluminosilicate (CaO–Al₂O₃–SiO₂) slags. Na₂O exhibits a stronger depolymerization ability in network structure than K₂O, which is reflected in the decrease of the proportion of bridging oxygen, cluster polymerization degree, and average ring size in the system. When a mass fraction of 0 to 10 pct Na₂O is individually added to the system, the viscosity decreases from 0.293 to 0.201 Pa s, and the thermal conductivity decreases from 1.174 to 1.037 W/m K. Similarly, when a mass fraction of 0 to 10 pct K₂O is individually added, the viscosity decreases from 0.293 to 0.231 Pa s, and the thermal conductivity decreases from 1.174 to 1.061 W/m K. When Na⁺/K⁺ coexist, a superposition effect occurs: increasing the K/Na ratio enhances charge compensation for [AlO₄] tetrahedra, stabilizes the network, and enlarges the ring size. Regarding the correlation between microscopic topological structure and properties, both viscosity and thermal conductivity decrease with the addition of Na₂O/K₂O. The average ring size of the oxygen network shows a strong positive linear correlation with viscosity and thermal conductivity. The regulatory effect of simultaneous Na/K addition on the viscosity and thermal conductivity of the CaO–SiO₂–Al₂O₃–Na₂O–K₂O (CSANK) system also follows a superposition effect. These findings provide theoretical support for precisely tuning mold flux performance by adjusting the Na/K addition ratio.</p>