NOVELTY - A multi-layer fluorine-containing crosslinked doped ion film comprises 2-40 layers of film formed by fluorine-containing ion exchange resin having equivalent weight value of 600-1300, and has conductivity of 40-150 mS/cm, extension strength of 10-60 MPa, and total thickness of 10-300 mu m. The layer(s) have crosslinked net-shaped structure, use a cellular film as the cellular reinforcing film, and are added with inorganic dopant having water protection function or proton exchange function, and with fiber.    USE - A multi-layer fluorine-containing crosslinked doped ion film.    ADVANTAGE - The inclusion of cellular film and reinforcing fiber improve the mechanical strength of the ion film. The existence of the water-protection inorganic dopant enables the electroconductibility of the obtained film at high or lower temperature to be far higher than an ordinary ion exchange film.    DETAILED DESCRIPTION - A multi-layer fluorine-containing crosslinked doped ion film comprises 2-40 layers of film formed by fluorine-containing ion exchange resin having equivalent weight value of 600-1300, and has conductivity of 40-150 mS/cm, extension strength of 10-60 MPa, and total thickness of 10-300 mu m. The layer(s) have crosslinked net-shaped structure, use a cellular film as the cellular reinforcing film, and are added with inorganic dopant with water protection function or proton exchange function, and fiber serving as a reinforcer. The crosslinked net-shaped structure can be of formula (I), (II), (III), (IV) and/or (V).    G1, G2=CF2 or O;    Rf=2-10C perfluorocarbon chain or perchlorofluorocarbon chain;    R=methylene or perfluoromethylene; and    n=0-10.    An INDEPENDENT CLAIM is included for a method for preparing the ion film, comprising forming each layer of the cellular film and fiber reinforcing multi-layer fluorine-containing crosslinked ion film by carrying out casting, extrusion, thermal press, spin coating, screen painting process and spray finishing or dipping process using fluorine-containing ion exchange resin, reinforcing fiber or inorganic dopant solution, or compounding fluorine-containing ion exchange resin, reinforcing fiber, or inorganic dopant solution with cellular film into a film; preparing multilayer film by using the formed single film; processing the formed multilayer film into crosslinked structure of formulae (I), (II), (III), (IV) and/or (V); and reacting formed crosslinked structure with alkali or acid solution. The processes such as casting, extrusion, thermal press, spin coating, screen painting, spray finishing or dipping comprise heat treating the film at 30-300 degrees C for 10-100 minutes. The crosslinked structure (I) is formed by using heat/light/electronic radiation, X ray, or free radical initiator in the presence of crosslinking agents of formula X2Rf7X-3. The crosslinked structure (II) and (III) are obtained by reacting Vikane(RTM: Sulfuryl fluoride), sulfonic acid chloride and sulfonic acid bromide type resin with ammonia, hydrazine or organic diamine or substances which can release ammonia, hydrazine or organic diamine through the chemical treatment. The crosslinked structure (IV) is obtained by treating fluorine-containing sulfoacid resin with chlorosulfonic acid. The crosslinked structure (V) is obtained by forming fluorine-containing sulfoacid resin, sulfonic-acid-chloride-containing resin or sulfonic-acid-bromide containing resin with nitrile group site under the action of heat or acid. The free radical initiator is organic peroxide or azo-type initiator, preferably perfluoroamine organic peroxide. The organic diamine is 1-10C alkyl or fluorine-containing alkyl diamine. The substances which can release ammonia, hydrazine or organic diamine through chemical treatment include (in)organic acid salt of ammonia, hydrazine or organic diamine, carbamide or guanidine. The acid is strong protonic acid such as sulfuric acid, trifluoromethanesulfonic acid, or phosphoric acid; or Lewis acid such as zinc chloride, ferric chloride, aluminum chloride, organic tin, organic antimony or organic tellurium.    X2, X3=Cl, Br or I;and    Rf7=perfluoroalkyl or fluorochloroalkyl.