The invention discloses a method for preparing a low-density ceramsite proppant from high-alumina fly ash. The method comprises the steps: (1) proportioning raw high-alumina fly ash, burnt high-alumina fly ash, clay, dolomite, talcum, river sand and an additive, and then, carrying out uniform mixing; adding water into the mixture, and carrying out wet grinding, so as to prepare mud; and then, drying the mud to prepare a powder material, and then, carrying out crushing, so as to prepare micropowder; (2) additionally, carrying out dry-process ball-milling or airflow crushing on raw high-alumina fly ash, so as to obtain micropowder with grain size smaller than 200 meshes; and (3) uniformly mixing the micropowder obtained in the step (1) and the micropowder obtained in the step (2), discontinuously spraying an aqueous solution containing the additive into the mixture, and carrying out granulating, so as to prepare sphere blanks; and then, carrying out polishing, semifinished product screening, baking, calcining and finished product screening, thereby obtaining a finished product. According to the method, the usage amount of the fly ash can reach 90%, the fly ash replaces other aluminiferous silicon raw materials such as bauxite, and the waste is utilized, so that the resource consumption is lowered; and the obtained fly ash proppant product is excellent in performance and stable in quality.