A method for extracting gallium from fly ash, comprising the following steps: a) crushing the fly ash to a particle size of passing through a sieve with the sieve opening size of 150 μ m (100 mesh), removing iron by wet magnetic separation, such that the ferric oxides content in the fly ash is reduced to 1.0wt% or less, then adding hydrochloride acid into the de-ironed fly ash to perform an acid-leaching reaction, and subjecting the reaction product to solid-liquid separation to yield a hydrochloric leachate having a pH value in the range of 1-3; b) adsorbing gallium in the hydrochloric leachate by passing the same through a column loading with a macro-porous cationic resin; eluting the column with water or hydrochloride acid as an eluting agent when the adsorption reaches saturation to obtain a gallium-containing eluent; c) adding sodium hydroxide solution into the gallium-containing eluent to react, separating precipitates after reaction by filtration to obtain a gallium-containing sodium metaaluminate solution; d) subjecting the gallium-containing sodium metaaluminate solution to carbonation by introducing carbon dioxide therein, and then separating gallium from most aluminum to obtain a gallium-aluminum double salt with the mass ratio of gallium to alumina being more than 1:340; and e) adding the gallium-aluminum double salt into a sodium hydroxide solution, subjecting the reactant to evaporation and concentration to obtain a base solution containing gallium and aluminum with the contents of gallium and alumina being 1mol/l or more respectively, and then electrolyzing the base solution to obtain metal gallium. a) crushing the fly ash to a particle size of passing through a sieve with the sieve opening size of 150 μ m (100 mesh), removing iron by wet magnetic separation, such that the ferric oxides content in the fly ash is reduced to 1.0wt% or less, then adding hydrochloride acid into the de-ironed fly ash to perform an acid-leaching reaction, and subjecting the reaction product to solid-liquid separation to yield a hydrochloric leachate having a pH value in the range of 1-3; b) adsorbing gallium in the hydrochloric leachate by passing the same through a column loading with a macro-porous cationic resin; eluting the column with water or hydrochloride acid as an eluting agent when the adsorption reaches saturation to obtain a gallium-containing eluent; c) adding sodium hydroxide solution into the gallium-containing eluent to react, separating precipitates after reaction by filtration to obtain a gallium-containing sodium metaaluminate solution; d) subjecting the gallium-containing sodium metaaluminate solution to carbonation by introducing carbon dioxide therein, and then separating gallium from most aluminum to obtain a gallium-aluminum double salt with the mass ratio of gallium to alumina being more than 1:340; and e) adding the gallium-aluminum double salt into a sodium hydroxide solution, subjecting the reactant to evaporation and concentration to obtain a base solution containing gallium and aluminum with the contents of gallium and alumina being 1mol/l or more respectively, and then electrolyzing the base solution to obtain metal gallium.