NOVELTY - A polyolefin diaphragm is produced by (A) preparing nucleating agent, (B) extruding, and (C) 8-40 times longitudinal stretching and transverse stretching at 90-160 degrees C, where forming density is less than or equal to 0.55g/cm3. The step (B) providing raw materials (wt.%): comprising metallocene compound catalyst of polypropylene homopolymer (50-80), polypropylene copolymer catalyzed metallocene complexes (2-50), and nucleating agent (1-4%), and extruding in extruder; subjecting in plastic extruding machine, and subjecting raw material to melting and plasticizing.    USE - Method for production polyolefin diaphragm for lithium battery (claimed).    ADVANTAGE - The produced diaphragm has high permeability, low density, has high transparency and high strength. The stretch ratio is 8-40 times. Density of the film is 0.55 g/cm3 or less, preferably 0.30 g/cm3.    DETAILED DESCRIPTION - Polyolefin diaphragm is produced by (A) preparing nucleating agent, (B) extruding, and (C) 8-40 times longitudinal stretching and transverse stretching at 90-160 degrees C, where forming density is less than or equal to 0.55g/cm3. The step (A) comprises preparing nucleating agent from (wt.%): N,N'-ethyl-2,6-naphthalene diamide (20-45), N,N-ethyl terephthalamide (30-60), diacid calcium salt (0.5-8), titanium dioxide (0.5-6), calcium carbonate and other inorganic salt (1-6), and polypropylene homopolymer (4-6). The step (B) providing raw materials (wt.%): comprising metallocene compound catalyst of polypropylene homopolymer (50-80), polypropylene copolymer catalyzed metallocene complexes (2-50), and nucleating agent (1-4%), and extruding in extruder; subjecting in plastic extruding machine, and subjecting raw material at 170-260 degrees C high temperature melting and plasticizing and extruding from a die, and putting in 100-150 degrees C chilling roller and cooling for 2-15 minutes; and melting and plasticizing for knife with heating device membrane adhered on chilling roller, performing heat preservation, and cooling casting sheet.