The invention discloses a preparation method of graphene-coated silicon dioxide nanoparticles. Graphite powder is taken as a raw material, graphene oxide with oxygen-containing functional groups is prepared with an improved Hummers method, the silicon dioxide nanoparticles are prepared with a hydrothermal method, a proper quantity of silane coupling agents are added to a solution containing silicon dioxide and uniformly stirred, the silane coupling agents are attached to the surfaces of silicon dioxide particles, and surface-modified silicon dioxide particles are obtained; graphene oxide is added to the modified silicon dioxide solution, and surfaces of the silicon dioxide particles are completely coated with graphene oxide under the interaction of functional groups. Finally, a reducing agent is added to the solution, graphene is formed by further removing the oxygen-containing functional groups of graphene oxide, and a composite with graphene completely coating silicon dioxide is prepared. The method has the advantages that a process is simple, the reaction time is short, regulation is easy and the like. The prepared composite has the characteristics of regular structure, high porosity, low density, good hydrophobicity and the like.