Manufacturing method of porous multilayered polyolefin

A manufacturing method of a polyolefin-based multilayer composite porous film as a battery separator, comprising:

• a) forming a composition including a polyolefin resin and diluent into a sheet;
• b) stretching the sheet and extracting the diluent to manufacture a film;
• c) performing heat-treatment on the manufactured film;
• and
• d) coating one surface or both surfaces of the heat-treated film with a coating solution containing a heat resistant resin, inorganic particles, and latex particles in an emulsion form that includes an acrylate group in which a glass transition temperature Tg is −60° C. to 0° C.,
• wherein step c) and step d) are continuously performed.