The invention provides a method used for producing alumina from fly ash. The method comprises following steps: high aluminum fly ash is subjected to dissolving out with hydrochloric acid at a high temperature, obtained aluminium chloride dissolving out solution and white clay are separated, and evaporation is carried out to obtain impurity containing AlCl<3>*6H<2>O crystal; the impurity containingAlCl<3>*6H<2>O crystal is subjected to hydrolysis at water vapour atmosphere at a hydrolysis temperature is controlled to be 200 to 850 DEG C to obtain an amorphous substance taking alumina as the main component; the amorphous substance is subjected to dissolving out with an alkali solution at normal pressure at a dissolving out temperature of 70 to 100 DEG C, or is subjected to dissolving out with an alkali solution at an increased pressure at a dissolving out temperature of 100 to 300 DEG C, a slag phase is removed through filtering, and a sodium aluminate solution is obtained at last; thesodium aluminate solution is filtered, diluted, and cooled for seed precipitation to obtain aluminium hydroxide. The methd is capable of reducing production cost of alumina from fly ash effectively, improving alumina quality, realizing utilization of large amount of solid waste, alleviating the shortage problem of bauxite resource of our state, and is suitable for application popularization in industrial production.