The invention relates to a preparation method of a graphene/water-based polyurethane nanocomposite material. The preparation method comprises the steps of after dehydrating a polyether polyol (N210) in vacuum, adding toluene diisocynate to the dehydrated polyether polyol, mixing evenly and reacting to obtain a prepolymer, adding dihydroxypropionic acid to introduce a hydrophilic group, reacting, cooling, dropwise adding acetone for diluting, adding triethylamine and stirring continuously, adding an aqueous solution of graphite oxide, deionized water and ethanediamine while stirring at a high speed for an emulsification reaction, carrying out reduced pressure distillation to obtain acetone and then dropwise adding a vitamin C solution for an in-situ reduction reaction to obtain a graphene/water-based polyurethane nanocomposite emulsion, and drying to obtain the graphene/water-based polyurethane nanocomposite material. The preparation method of the graphene/water-based polyurethane nanocomposite material is simple and environmental friend in process, and applicable to large-scale production, and can be applied to the fields of electrostatic protection, anticorrosive coating, building coating and the like.