The invention provides a vanadium solution dephosphorization process and system used during production of vanadium pentoxide by vanadium slag. The dephosphorization system comprises a phosphate removing agent storage tank, a phosphate removing agent high-level gauging tank, a distribution vehicle, a first-grade thickener, a second-grade thickener, a transfer pump and a vacuum filtration pump. The process comprises the steps that clinker obtained by roasting the vanadium slag is loaded in the distribution vehicle and is leached, a leaching solution is delivered into the first-grade thickener through the vacuum filtration pump, the clinker in the distribution vehicle is washed with a phosphate removing agent in the phosphate removing agent storage tank in a sprayed manner to be subjected to primary dephosphorization and then continues being washed with water in the sprayed manner, and the leaching solution in the first-grade thickener continuously overflows into the second-grade thickener; a steam stirring solution is introduced into the second-grade thickener, the phosphate removing agent is delivered into the phosphate removing agent high-level gauging tank through the transfer pump, and the phosphate removing agent is delivered into the second-grade thickener to conduct secondary dephosphorization; and a qualified vanadium solution is obtained after the second-grade thickener stands still and the solution is clarified. The process and system have the advantages that the equipment utilization rate is high, the structure is reasonable, operation is convenient, consumption of the phosphate removing agent is little, less waste residues are produced in the dephosphorization process, and the vanadium recovery rate is high.