For the purpose of the recovery of the high-purity vanadium product in leaching solution, solvent extraction has been considered as a promising approach. However, the vanadium species varied in different concentrations and pH values in aqueous solution, thus affecting the extraction yield or the reaction product in the process. In this paper, the main species of vanadium in solutions were determined with the equilibrium constants. The extraction reactions were determined based on determined species, then the hydrogen bond association mechanism of the reaction as well as the possible structures of the vanadium complexes were proposed and discussed in detail. This study established a systematic methodology for understanding the transition metal speciation in aqueous solutions as well as the extraction reactions, and envisaged the insights into the mechanism of the transition metal solvent extraction by primary amines.