The invention discloses a method for preparing a starch-modified hydroxyethyl acrylate and aluminium complex tanning agent. The method comprises the following steps: weighing starch, deionized water A, sodium bisulfate, CMC, SDS, silicone oil, op-10, mercaptan and ferrous sulphate, adding starch, deionized water A, sodium bisulfate, CMC, SDS, silicone oil, op-10, mercaptan and ferrous sulphate in a flask, stirring the materials and heating the materials to the temperature of 50-60 DEG C, adding hydrogen peroxide A, performing isothermal stirring reaction for 30-60 min, heating the materials to the temperature of 80-96 DEG C, gelatinizing the materials for 30-90 min, then cooling the material to the temperature of 70-80 DEG C, adding an initiator dropping by drop and a monomer, performing isothermal stirring reaction for 30-120 min, and cooling the material to room temperature to obtain the starch-modified hydroxyethyl acrylate and aluminium complex tanning agent. The starch-modified hydroxyethyl acrylate and aluminium complex tanning agent can effectively increase the mechanical property, contraction temperature and water proofness of the leather, and tanning removal is difficultly carried out.