A process for preparing V2O5 from the used catalyst containing V includes such steps as removing deposited oil from said catalyst, pulverizing, immersing in water, oxidizing, adding alkali to regulate pH=8.5-9.5, extracting at 50-60 deg.C for 1-2 hr, solid-liquid separation, recovering the solution of sodium vanadate and sodium molybdate, washing filtered dregs, calcining in rotary furnace, dissolving the calcined material in water, stirring, solid-liquid separation, recovering the solution of sodium vanadate and sodium molybdate, collecting said solution, removing impurity P, adding ammonium chloride to generate ammonium metavanadate deposit, solid-liquid separation, adding ammonium metavanadate in flake-making furnace, decomposing at 800-850 deg.C to obtain fused V2O5, and preparing V2O5 flakes.