The invention discloses a method for preparing iron-free aluminum sulfate and superfine active white carbon black with bauxite, crushing the bauxite and removing dissociative iron source by magnetic separation, and then reacting with vitriol; adding in dithiocarbamate with medium and high molecular weights and multiple functionalities to remove iron ions by solid phase reaction, and filtering, where the filtrate is iron-free aluminum sulfate; washing filter residue with alkaline water solution, surface active agent water solution, and tap water, respectively, to neutralize it, then after reacting with alkali, filtering, making filtrate, inorganic acid and active particles react mutually, filtering, water-washing, and drying to obtain the superfine active white carbon black. And the method has simple process, and low cost, applied to industrialized production, where the iron content of the prepared aluminum sulfate is less than 15 ppm, and the grain size, specific surface area, tensile strength, added value of the superfine white carbon black are 0.5-5 mum, greater than 200 m2 / g, higher than 17.0 MPa, and high, respectively.