The electrochemical and Mg ion diffusion properties of tavorite-Mg_0.5FeSO₄F were studied by using first principles calculations. A discharge voltage of about 2.52 V versus Mg/Mg²⁺ corresponding to the redox couples of Fe³⁺/Fe²⁺ was predicted for tavorite-Mg_0.5FeSO₄F, and the experimental diffusion coefficient for the Mg-vacancy in Mg_0.5−xFeSO₄F is expected to be of the same order of magnitude as that of the Li-vacancy in Li_1−xFeSO₄F.