The invention relates to a method for producing ammonium metavanadate by using a waste catalytic cracking catalyst in an oil refinery. The method comprises the following steps: mixing the waste catalyst with sulfuric acid, calcium fluoride and water in a mixer, feeding into a curing cabin, and curing in the curing cabin; pulpifying the mixed materials with water; pumping the pulpified liquid into a leaching tank, and heating and stirring for leaching; pumping into a plate filter press for liquid-solid separation, feeding the leachate into a crystallization tank, and adding ammonium sulfate to crystallize; and performing liquid-solid separation, thereby obtaining an aluminum ammonium sulfate product and crystallization master batch; and adding ammonium carbonate into the crystallization master batch to adjust the pH value, adding ammonium persulfate, adding ammonium carbonate to adjust the pH value, heating to react, pumping into the filter press, and performing liquid-solid separation, thereby obtaining ammonium metavanadate. The separated liquid can be also fed into a lanthanum-cerium deposition tank, and ammonium oxalate is added to react to obtain lanthanum oxalate and cerous oxalate, or the separated liquid is fed into a nickel deposition tank, and ammonium sulfide is added to react to obtain nickel sulfide. By adopting the method, the waste catalytic cracking catalyst in the oil refinery can be reused for producing ammonium metavanadate, the problems that the environment can be polluted by the waste catalyst and the land can be occupied are effectively solved, the purity of the produced ammonium metavanadate is even greater than 99%, and the recycling efficiency is high.