The invention discloses a hydrophilic polyvinylidene fluoride modified separation membrane and a preparation method thereof. The separation membrane is prepared from polyvinylidene fluoride, a polyvinylidene fluoride solvent, a carbon oxide carbon nano tube / graphene oxide and a pore-forming agent. According to the hydrophilic polyvinylidene fluoride modified separation membrane, on one hand, hydrophilicity of the separation membrane is enhanced through oxygen-containing functional groups in the carbon oxide carbon nano tube and graphene oxide, on the other hand, graphene oxide of a sheet structure enters a carbon oxide carbon nano tube network of a tubular structure for mutual intercalation to form a stable sandwich layered structure, therefore, agglomeration of the same nano structure bodies can be effectively inhibited, and migration and assembly of graphene oxide to the surface of a composite membrane are facilitated, and the contact area of the carbon oxide carbon nano tube and graphene oxide and macromolecule matrix in the composite membrane is remarkably improved, and thus, the hydrophilicity and anti-pollution capacity of the membrane are enhanced, so that the water flux of the membrane is substantially improved. In addition, the preparation method is simple in operation technology and is easily carried out.