The invention discloses a starch-grafted waterborne polyurethane sand fixing agent and a preparation method thereof. The sand fixing agent is a starch-grafted waterborne polyurethane dispersion liquid of which the viscosity is 20-500 mPa.s at the temperature of 25 DEG C, the solid content is 30-45 percent by weight, the pH value is 6-8, and the storage stability is higher than six months; and the Shore hardness of a filmed dispersion liquid is 35-45. The sand fixing agent is obtained by undergoing a polymerization reaction on polyether polyol, diisocyanate, dimethylolpropionic acid, a neutralizing agent, starch, a latent solvent and a catalyst for forming a performed polymer and adding into deionized water for emulsifying. The starch-grafted waterborne polyurethane sand fixing agent has the advantages of degradability, nontoxicity, non-flammability, use safety, environmental friendliness, high nutrition and the like, and can be widely applied in the fields of agriculture and forestry as an environmentally-friendly nutritional sand fixing agent.