Provided a method for preparing metallurgical-grade alumina by using fluidized-bed fly ash, comprising: a) removing iron by wet magnetic separation after crushing the fly ash; b) reacting the fly ash after magnetic separation with hydrochloric acid to obtain a hydrochloric leachate; c) passing the hydrochloric leachate through macro-porous cationic resin to deeply remove iron to obtain a refined aluminum chloride solution; d) concentrating and crystallizing the refined aluminum chloride solution to obtain an aluminum chloride crystal; and e) calcining the aluminum chloride crystal to obtain the metallurgical-grade alumina. The method is simple, the procedure is easy to be controlled, the extraction efficiency of alumina is high, the production coast is low, and the product quality is steady.