The invention discloses a method for producing alumina by curing fly ash with sulphuric acid, belonging to the technical field of comprehensive utilization of the fly ash. The method comprises the following steps: uniformly mixing a proper amount of concentrated sulfuric acid and the fly ash, then carrying out curing so as to obtain a sulfated clinker, then leaching the clinker with an aluminum sulfate crystallized mother liquor or water so as to obtain an aluminum sulfate and high-silicon slag, subjecting the aluminum sulfate solution to evaporation, concentration, crystallization, drying and dehydration so as to obtain aluminum sulfate, subjecting obtained aluminum sulfate and a proper amount of a reducing agent to rapid reduction and calcination so as to obtain crude alumina, then treating the crude alumina by adopting a low-temperature Bayer process so as to produce metallurgical-grade alumina, wherein the obtained high-silicon slag can be leached by sodium hydroxide to produce white carbon black or active calcium silicate. The method provided by the invention has the advantages of high aluminum recovery rate, easily-available equipment and materials, good alumina product quality, etc.; and the slag obtained by leaching of aluminum is the high-silicon slag with good alkali-soluble activity, and can be used for further production of a variety of high-value-added silicon products.