The invention relates to a method for producing sandy alumina, especially to a method for producing sandy alumina by high-alumina fly ash. The method for producing sandy alumina by fly ash comprises the following steps of: carrying out acid-leaching on the fly ash raw material by using acid, followed by desiliconization and crystal thermal decomposition to obtain crude alumina, carrying out alkali dissolution on the crude alumina by using an alkali regulating solution, carrying out liquid-solid separation on the dissolved slurry, filtering and removing slag to obtain a sodium aluminate solution, adding aluminium hydroxide as seed into the sodium aluminate solution, cooling the sodium aluminate solution for seed precipitation so as to obtain an aluminium hydroxide precipitate, carrying out liquid-solid separation on the aluminium hydroxide precipitate, followed by washing to obtain aluminium hydroxide, and roasting aluminium hydroxide to obtain sandy alumina. By a serial production technology of preparing crude alumina by an acid method and preparing sandy alumina by an alkali method, the material cycle for alumina extraction by the acid method is less with less amount of slag; energy consumption for low-temperature alkali dissolution is low; the flow and material adoption are simple; and the quality of aluminium hydroxide and the alumina product prepared by the seed precipitation technology is high.