Abstract: The electrical conductivity of the CaO-Al₂O₃-SiO₂ system was modeled based on the concept of optical basicity. The model can reflect the effect of the amphoteric behavior of Al₂O₃on the electrical conductivity and the phenomenon that the electrical conductivity decreases when substituting Al₂O₃for SiO₂. According to the comparison between the diffusion coefficients of different ions, it is indicated that the charge transport process is mainly completed by Ca²⁺. The self-diffusion coefficient of Ca²⁺ was calculated by the estimated electrical conductivity and the Nernst-Einstein equation. The deviation between the calculated diffusion coefficient and that measured by a tracer atom method was discussed, and a theoretical interpretation for the decrease of deviation with increasing temperature was also given.