The invention discloses a method for preparing etherification-oxidation-grafting multi-modified starch. It uses original starch as raw material, adds etherifying agent, oxidant and composite catalyst, uses microwave semi-dry method to complete the etherification oxidation reaction in one step, and then uses The obtained etherified oxidized starch is used as raw material, initiator, alkaline catalyst and composite vinyl monomer are added, and the graft copolymerization is carried out in a microwave reactor using an open system method. This invention organically combines the three denaturation methods of etherification, oxidation, and grafting, and connects a variety of reactive groups to the starch molecular structure to maximize strengths and avoid weaknesses, and complement each other's advantages. By adjusting the process formula, a series of reactive group ratios can be obtained Multiple modified starches with different grafting rates. The product has various excellent properties of carboxymethyl etherification and / or hydroxyalkyl etherification, oxidation, and grafted starch, and can be used in papermaking, food, textiles, daily chemicals, polymer flocculants, highly absorbent materials, and oil fields. Chemical materials, degradable plastic films and plastics.