The reaction between HS- and pentavalent vanadium V(V) and its effect factors, such as reactant concentration, reaction temperature, and the pH value in tannin extract desulfurization technology has been researched in this article. The results show that the reaction between HS- and V(V) is a quick reaction process. When the initial concentration of V(V) increases, the reaction speed accelerates, and the equilibrium conversion of HS- rises. The effect of reaction temperature is smaller in the operation range of tannin extract desulfurization technology, and the reaction speed slows with the pH value enhancing. Additionally, a new reaction mechanism on the reaction between HS- and V(V) was proposed by analyzing the experimental phenomena and the solid product.