The invention discloses a preparation method of a PVDF (Polyvinylidene Fluoride) separating membrane, polyvinylidene fluoride is adopted as a raw material of a membrane, and the preparation steps of the polyvinylidene fluoride comprise: 1) putting 1 to 2 parts by weight of hydroxy propyl cellulose, 2.4 parts by weight of hydrogen peroxide and 3.7 parts by weight of inorganic base solution into a reaction still, uniformly mixing, then putting 1.8 parts by weight of dodecyltrimethylammonium chloride, 9.7 parts by weight of hexafluoroethane solvent and 1.8 parts by weight of chloroacetyl chloride solution into the reaction still, stirring and reacting at -5.5 DEG C for 39 minutes; 2) putting 3.7 parts by weight of fatty acid methyl ester sulfonate, 5.7 parts by weight of N-methylpyrrolidone solution, 63 parts by weight of vinylidene fluoride monomer and 2.6 parts by weight of 2,2,3-trimethylpentane into the reaction still, stirring and reacting at 14 DEG C, and performing a termination reaction when the pressure is decreased to 0.23 MPa or less; 3) filtering, washing and drying to obtain powder-like polyvinylidene fluoride. The separating membrane prepared by the invention has the properties of corrosion resistance, heat resistance, cold resistance, oxidation resistance and weather resistance.