NOVELTY - A flexible packaging material preparing method involves cleaning aluminum foil, pre-treating the aluminum foil in a side surface of the protective layer, preparing heat seal layer. The heat seal layer is laminated on aluminum foil to form first composite layer. The first composite layer is allowed for plasticizing process. The first composite plastic layer is placed in cooling section, followed by winding the cooled material at 20-70 degrees C, and extruding outer protective layer on the cooled material by using co-extrusion laminating machine at 20-70 degrees C to obtain the finished product.    USE - Method for preparing flexible packaging material for use in lithium-ion battery.    ADVANTAGE - The method enables preparing flexible packaging material with improved mechanical property, reduced brittleness and improved cold stamping performance.    DETAILED DESCRIPTION - A flexible packaging material preparing method involves cleaning aluminum foil, pre-treating the aluminum foil in a side surface of the protective layer, preparing heat seal layer at 100-150 degrees C. The heat seal layer is laminated on aluminum foil in the side of inner protective layer through hot coating machine at 140-160 degrees C to form a first composite layer. The first composite layer is allowed for plasticizing process at 180-210 degrees C to obtain first composite plastic layer. The first composite plastic layer is placed in cooling section having first cooling section of 140-155 degrees C for 1-5 minutes and second cooling section of 100-130 degrees C for 1-5 minutes to obtain a cooled material, followed by winding the cooled material at 20-70 degrees C, and extruding outer protective layer on the cooled material by using co-extrusion laminating machine at 20-70 degrees C to obtain the finished product, where the heat seal layer comprises laminated cast polyolefin film layer and modified polyolefin film layer, the modified polyolefin film layer is arranged in the aluminum foil in the side surface of the protective layer.