The invention relates to a method for preparing vanadium pentoxide from sulfuric acid leach liquor of stone coal vanadium ore, particularly a method for preparing high-purity vanadium pentoxide from sulfuric acid leach liquor of low-impurity-content stone coal vanadium ore. The method is characterized by sequentially comprising the following steps: (1) extracting leach liquor, which is obtained by leaching stone coal vanadium ore with sulfuric acid, to remove impurities; (2) carrying out back extraction on sulfuric acid to carry an organic phase; (3) oxidizing the back extraction liquor; (4) carrying out hydrolysis to precipitate vanadium; and (5) calcining the vanadium precipitate slag to obtain the vanadium pentoxide. Compared with the traditional technique, by using oxydol, persulfuric acid and the like as oxidants in the oxidation process, the method provided by the invention can avoid introducing other impurity cations, thereby ensuring the purity of the product vanadium pentoxide. Compared with the traditional ammonium-salt vanadium-precipitation technique, the method provided by the invention saves the alkali consumption required by neutralization. The purity of the prepared vanadium pentoxide is up to 99.9%, and the recovery rate of vanadium is up to above 98%; and meanwhile, the invention can implement no pollution and cyclic utilization of the back extraction agent.