Abstract: The polyvinylidene fluoride (PVDF) flat microporous membrane was prepared via thermally induced phase separation (TIPS) method using dimethyl phthalate (DMP) as the diluent. The crystallization of different PVDF/DMP systems were analyzed by the differential scanning calorimetry (DSC). The membrane was characterized by pure water permeability, porosity, bubble point, mean pore radius and tensile strength. Results show that the crystallization temperature decreases with the increasing of diluent content. The PVDF/DMP system exhibits solid-liquid phase separation. With the increasing of polymer concentration, pure water permeability, porosity, maximum pore size and mean pore radius decrease. The tensile strength of the membrane reduces with the diluent content increasing, and an obvious inflexion appeares when the mass fraction of diluent is 0.70.