The invention discloses a continuous preparation method of a porous composite ion membrane, and belongs to the technical field of all-vanadium redox flow batteries. According to the method, perfluorinated sulfonic acid resin with good chemical stability is used as a membrane material main body; polymers and additives with different functions are added and put into an extruder hopper for melting, plasticizing and extrusion molding; the molded membrane is cooled in a plurality of temperature sections, wherein the temperature is sequentially reduced from high to low; the cooled membrane enters anextracting solution for extraction, the additives are extracted to form pores, and finally the extracted membrane is washed in deionized water, and rolled for membrane formation to form the porous composite ion membrane. The continuous preparation process of the ion composite membrane is simple, and the prepared membrane is low in swelling, good in dimensional stability, high in mechanical strength, low in vanadium ion permeability, good in chemical and thermal stability, simple in operation and low in requirements on equipment and operators, and can be applied to all-vanadium redox flow batteries (VRB).