The invention provides a production method for a porous composite membrane. The method is used for processing a first porous membrane and a second porous membrane. The method comprises the following steps that: a pressing unit, a forming unit and a cooling unit are provided; the first porous membrane and the second porous membrane are crossed at an angle; the first porous membrane and the second porous membrane are overlaid to form a porous composite membrane semi-finished product; the porous composite membrane semi-finished product is pressed by the pressing unit at the temperature of T1 and under the tension of S1; the porous composite membrane semi-finished product is subjected to pressure relief forming by the forming unit at the temperature of T2; the porous composite membrane semi-finished product is maintained under the tension of S3 by the cooling unit at the temperature of T3; the porous composite membrane finished product is finished. Lithium battery separation films with large puncture resistance can be produced through the method, and tensile strength, air permeability time, pore size and stripping resistance of the separation films are all taken into account.