The invention discloses a waterborne polyurethane/dopamine modified graphene nano-composite emulsion preparation method and belongs to the field of organic-inorganic nano-composite materials. According to the preparation method, an improved Hummers method is utilized to prepare graphene oxide dispersion liquid at first, and then dopamine is utilized to surface modify the graphene oxide and compounded with waterborne polyurethane to prepare a waterborne polyurethane/dopamine modified graphene nano-composite emulsion. According to the preparation method disclosed by the invention, low polymer polyalcohol is utilized as a soft segment, isocyanate compound is utilized as a hard segment, and the dopamine modified graphene oxide dispersion liquid is guided into a waterborne polyurethane preparation process in site to prepare the waterborne polyurethane/dopamine modified graphene nano-composite emulsion. As the dopamine modified graphene is guided into, mechanical property, static resistance,conductivity, electromagnetic shielding, thermal conductivity, chemical resistance, corrosion resistance and the like of waterborne polyurethane membranes and coatings are effectively improved. The waterborne polyurethane/dopamine modified graphene nano-composite emulsion and rubber powder have a better application prospect in the fields of coatings, adhesives, printing ink, surface treating agents, elastomer, foam materials, functional films and the like.