Keratin grafted with quaternary ammonium salt cationic reagent can improve the cationic degree. In the experiment, a cationic keratin protein was prepared by introducing a quaternary ammonium into the keratin molecule. The cationic keratin was used as flocculant, the flocculation performance of several common leather auxiliaries was investigated, and the flocculation performance of the flocculant was studied. The experimental results show that the effect of some kinds of leather auxiliaries is good, among them, the flocculation effect of the dye is the best, the flocculation rate can reach more than 90%.When The floc is used as leather filling material, the thickness of the leather can reach 15.12%, the tensile strength is increased from 15.81MPa to 16.40MPa, and the elongation at break of the blank is also increased from 5 to 5, 8 to 9, and the ideal filling effect is improved.