An aluminium oxide preparation and comprehensive utilization method through chlorination and electrolysis of fly ash comprises the following steps: chloridizing and separating fly ash to obtain anhydrous aluminium chloride, silicon tetrachloride and gallium chloride; converting anhydrous aluminium chloride into an aluminium chloride water solution; controlling the voltage and the current density, and electrolyzing the aluminium chloride water solution to obtain aluminium hydroxide, hydrogen and chlorine; returning chlorine generated by electrolysis to a chlorination section; roasting aluminium hydroxide to obtain metallurgical-grade/chemical aluminium oxide; and performing distillation purification on silicon tetrachloride to generate polycrystalline silicon and zinc chloride. The aluminium oxide preparation and comprehensive utilization method is low in cost, cheap and easily accessible in raw material, simple in operation process, high in degree of automation and high in product purity, and the adopted raw materials, zinc, chlorine and the like, can be recycled.