The invention discloses a method for preparing
polyvinylidene fluoride ultra-
filtration membranes. The method includes the steps of mixing the
polyvinylidene fluoride with diluents, and heating the mixture to form a homogeneous phase solution, wherein the diluents are a mixture of a
solvent and a non-
solvent of the
polyvinylidene fluoride, and at least one of the
solvent and the non-solvent of the polyvinylidene
fluoride can be dissolved in water; subjecting the homogeneous phase solution to knife
coating on a supporting screen to form a plate-shaped membrane
casting solution or to be spinned into a membrane
casting solution in a hollow
fiber shape by a spinneret, submerging the membrane
casting solution into a cooling liquid to be cooled, subjecting the membrane casting solution to phase separation and solidifying into membranes; extracting the diluents in the membranes through an extracting agent to obtain the polyvinylidene
fluoride membranes. Sections of the polyvinylidene
fluoride membranes are in a homogeneous spongeous structure with bore diameters in a range of 0.02 to 4 microns, and the membranes have surface
layers with surface bore diameters
ranging from 2 nanometers to 100 nanometers. Simultaneously, the polyvinylidene fluoride ultra-
filtration membranes have the advantages of high strength,
porosity, flux and separation accuracy.