In order to efficiently extract vanadium and remove phosphorus from acidic leaching solutions of vanadium-bearing converter slag, thermodynamic equilibrium diagrams of V-H2O and V-P-H2O systems were analyzed to understand the transformation rules of the single-core ion, isopolyacid ion, and heteropolyacid ion with changing pH values. The results revealed that, vanadium were predominately present as VO2+ as pH ranging from 0 to 0.5 in the V-H2O and V-P-H2O systems. As the solution became more alkaline, VO2+ gradually transformed into isopolyvanadate anions (V10O286-, HV10O285- and H2V10O284-) in the V-H2O solution ([V5+] = 0.1 mol/L), with maximum mole fraction of Sigma V-10 (sum of isopolyvanadate anions containing 10 vanadium) being nearly 100% when pH = 2-5.5. While in the V-P-H2O solution ([V5+] = 0.1 mol/L, [P 6+ ] = 0.01 mol/L), VO2+ first transformed into P-V heteropolyacid anions (H5PV14O424-, H4PV14O425- and H3PV14O426-) as 1 <= pH <= 3.5 due to the existence of phosphorus, and the maximum mole fraction of Sigma PV14 (sum of P-V heteropolyacid anions) reached 90.35% at pH = 2. The P-V heteropolyacid anions then transformed into isopolyvanadate anions when pH value ranged from 3.5 to 7, and the maximum mole fraction of Sigma V-10 was 100% at pH = 5. Verification experiments of the solvent extraction on vanadium and phosphorus in the V-H2O ([V6+] = 0.1 mol/L) and V-P-H2O ([V5+] = 0.1 mol/L, (P5+] = 0.01 mol/L) systems were conducted with trialkylamineN235. Experimental results showed that the extraction rates of Sigma V-10 + Sigma PV14 in the V-P-H2O solution were always higher than those of Sigma V-10 in the V-H2O solution as 0.5 <= pH <= 1.5, and a portion of phosphorus element was extracted in the form of H2PO4- + Sigma PV14, which was highly consistent with the thermodynamic analyses. Finally, a process flow sheet was established on the P-V separation followed by efficient phosphorus removal and extraction of vanadium.