The invention provides a method for preparing low-ferrum crystalline aluminium chloride from coal ash, which comprises the following steps of: 1, crushing the coal ash, and performing wet magnetic separation on the crushed coal ash to remove ferrum; 2, reacting the coal ash subjected to ferrum removal and hydrochloric acid to obtain pickle liquor; 3, concentrating the pickle liquor under a reduced pressure, cooling and crystallizing to obtain crystalline aluminium chloride slurry; and 4, performing solid-liquid separation on the crystalline aluminium chloride slurry, rinsing with leacheate, performing solid-liquid separation and drying to obtain low-ferrum crystalline aluminium chloride products. The method has the advantages of wide raw material source, low cost, simple operation step, easily controlled production process, stable product quality and the like. The ferrum (Fe) content of the crystalline aluminium chloride products prepared by the method of the invention is no more than 0.025 weight percent.