The invention provides a method for preparing protein fillers used for tanning by taking tanning chrome containing scrap materials as materials. The invention is characterized in that chrome containing scrap materials obtained from pieced wet blue are ground, and 100 portions by weight of chrome containing scrap materials are picked up and soaked in an alkali compound solution with the concentration of between 0.1 and 2wt percent, which at least submerges chrome containing scrap materials, for 10 to 48 hours, and the chrome containing scrap materials are drained, and the pretreated chrome containing scrap materials are put in a reaction kettle provided with a stirrer, a thermometer and a reflux condenser, and 6 to 20 portions by weight of alkali compounds and water at least submerging chrome containing scrap materials are added, and the reaction kettle is heated to a temperature of between 50 and 95 DEG C and keeps the temperature for 2 to 20 hours, and the thick liquids with deep color are obtained, and the pH value of the thick liquids is adjusted to between 7 and 10 by an inorganic acid after the thick liquids are cooled, and the thick liquids are filtered, and the filtrate with the solid content of between 10 and 20 percent, which is rich in containing collagen polypeptides, and the filter residues are obtained, and finally the protein fillers for tanning are obtained after the filtrate is condensed and dried; the filter residues are added with 100 to 150 portions by weight of water and has the pH value adjusted to between 2 and 3 by the inorganic acid solution, which obtains a Cr2(SO4)3 green solution used for the chroming agent.