The invention discloses a preparation method of a starch water-retaining agent with high gel strength. The preparation method is characterized by comprising the following steps of gelatinizing wheat starch, preparing a sodium acrylate solution under an ice bath condition, adding maleic acid, N,N-methylene bisacrylamide, ammonium persulfate and a sodium acrylate solution into the gelatinized wheat starch to obtain a mixed solution, stirring the mixed solution for graft copolymerization to form a copolymerization product, pouring the copolymerization product into a tetrafluoroethylene board for drying treatment, and obtaining the starch water-retaining agent with the high gel strength, wherein maleic acid can be changed to kaoline or kieselguhr. According to the method, maleic acid, kaoline or kieselguhr serves as a raw material to prepare the starch water-retaining agent, so that the prepared starch water-retaining agent is high in gel strength, biodegradability, water absorption velocity and salt tolerance, and the preparation method is simple and non-pollution and can be used for industrial production.