Probing the underlying conduction mechanism with a reliable and detailed description is important for optimizing solid oxide electrolyte materials. Herein, an equation has been proposed for the first time to quantitatively predict the vacancy preference for a given cation in a fluorite structure. The results derived from the equation are consistent with NMR observations. By investigating the local structure and conductivity in CeO2-ZrO2-Y2O3 ternary system from both molecular dynamics simulations and experiments, we have developed a theoretical framework to elucidate the mechanism of the dopant properties on ion transport in yttria-doped ceria-zirconia system. Lower vacancy preference mismatch between the host and a dopant is found to give rise to a better homogeneity of vacancy distribution, indicated by less vacancy cluster formation thereby resulting in a higher conductivity. This comprehension concerning the dopant properties-conductivity correlation should help in the development of more effective and selective oxide electrolyte for the fuel cells and other applications.