The invention relates to a preparation method of a graphene modified water-soluble isocyanate curing agent. The preparation method particularly comprises the following steps: (1) performing pre-dispersion treatment on graphene: adding the graphene powder in propylene glycol methyl ether acetate while stirring, stirring the solution at high speed until the solution is uniform after all the graphene powder is added, and performing ultrasonic dispersion to obtain graphene dispersion liquid, wherein the graphene content is 0.006 to 0.04wt%; (2) preparing the graphene modified water-soluble isocyanate curing agent: adding the graphene dispersion liquid, a polyfunctional hydroxyl component, an isocyanate monomer, a hydrophilic agent and a solvent into a four-neck flask, heating to 70 to 80 DEG C in water bath, reacting for 5 to 10 hours, adding an end-capping agent, reacting for 4 to 5 hours, cooling to 30 DEG C, and adding lactic acid and neutralizing to prepare the graphene modified water-soluble isocyanate curing agent. According to one-step in-situ graft polymerization, the preparation method is high in efficiency and simple to operate, and the function of improving the corrosion resistance and the wear resistance of coating by the graphene is realized.