The mechanism governing de-oxidation of vanadium metal is regarded as fundamental knowledge; however, it has not been elucidated in existing literature. In this paper, the thermodynamic data of V-H-O systems were summarized, and the Gibbs free energies of the main compounds were calculated. Consequently, the de-oxidation limits of different reductants in a VO system were evaluated, namely: Si, Al, and Mg. It was observed that Si could not remove an O content of less than 7.27 wt% from V. However, Al was the stronger reducing agent; it could remove O contents of up to 0.01 and 0.1 wt% at 800 and 1050?C, respectively. Nevertheless, Mg exhibited the best reducing properties as it could remove less than 0.01 wt% of O at 1100?C. The addition of H2 rendered the V-O solid solution unstable to a certain extent, thereby indicating that H2 facilitated de-oxygenation. Furthermore, the results obtained by analyzing the equilibrium conditions were in accordance with the results of the de-oxidation limit in the V-O system. In other words, this study demonstrated that oxygen in vanadium can be effectively controlled by changing the reductant dosage and temperature.