The invention provides a secondary battery composite membrane, a preparation method thereof and a secondary battery. The secondary battery composite membrane comprises an electric-insulated substrate layer and a conducting layer which is bonded to the surface of the electric-insulated substrate layer, and the conducting layer comprises conducting material, and the thickness of the conducting layer is 5 to 50 microns. The preparation method of the secondary battery composite membrane comprises the steps as follows: preparing dispersion liquid or slurry with conducting material, forming the conducting layer on the surface of the electric-insulated substrate layer by using the dispersion liquid or slurry with conducting material, drying and shaping the composite membrane, pressing the dried and shaped composite membrane. The membrane of the secondary battery uses the secondary battery composite membrane of the invention. The secondary battery composite membrane of the invention can be used for effectively preventing electrode material from falling off from a current collector so that the current collector can be used for charging and discharging continuously. The preparation method of the invention is high in production efficiency and can be applied in industrial production. The cycle life of the secondary battery is long.