This article investigated the saturated solubility of MgO in converter vanadium slag and its influencing factors. The experimental results of MgO dissolution equilibrium are consistent with the theoretical calculation results. The results show that in MgO saturated vanadium slag, MgO mainly exists in MgV2O4 and MgSiO3. The increase of V2O3 content or the decrease of the FeO/SiO2 ratio is beneficial to increasing the saturated solubility of MgO in the FeO-SiO2-V2O3 slag system. The saturated solubility of MgO in vanadium slag increases from 7.5 to 8.0 wt.% when the temperature increases from 1633 to 1753 K. In addition, the solubility of MgO also increases with the increase of TiO2 and Al2O3 content and decreases with the increase of MnO content.