The invention discloses a synthetic method of a graphene reverse osmosis composite membrane, and belongs to the technical field of materials. The method comprises the following steps: firstly preparing amido graphene , then mixing the amido graphene with a solvent, carrying out ultrasonic dispersion, adding unsaturated acyl chloride and triethylamine in sequence, stirring and heating to react; filtering, and washing to obtain an intermediate; adding monomers into a mixture of the intermediate and the solvent, stirring uniformly, then adding an initiator, heating and stirring to form the membrane. According to the reverse osmosis composite membrane prepared by the method, polymers are dispersed among layers, the polymers maintain the dispersion of the layers while the mechanical strength of the membrane is improved, and the reverse osmosis performance of graphene is also retained. The reverse osmosis composite membrane is good in performance, and fundamentally overcomes the defect such as small graphene specific surface area caused by excessive stacking of the layers in the graphene synthesis process. The synthetic graphene reverse osmosis composite membrane can be used for water treatment in the fields of electrons, information, energy resources, materials, biological medicine and the like.