Provided is a manufacturing method of a polyolefin-based multilayer composite porous film, including: a) forming a composition including a polyolefin resin and diluent to 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, wherein step c) and step d) are continuously performed.