The present invention provides a system and method for purifying vanadium pentoxide. Industrial grade vanadium pentoxide is converted to vanadium oxytrichloride by low temperature fluidizing chlorination, wherein chlorinating gas is preheated via heat exchange between fluidizing gas and chlorination flue gas, and an appropriate amount of air is added to enable a part of carbon powder to combust so as to achieve a balanced heat supply during the chlorination, thereby increasing the efficiency of chlorination and ensuring good selectivity in low temperature chlorination. The vanadium oxytrichloride is purified by rectification, and then subjected to plasma oxidation, thereby obtaining a high-purity vanadium pentoxide product and chlorine gas. The chlorine gas is returned for low temperature chlorination. The system and method have advantages of favorable adaptability to a raw material, no discharge of contaminated wastewater, low energy consumption and chlorine consumption in production, stable product quality and so on.