TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Substance: The active substance (E) is catalyst, which a metal containing platinum.Preferred Process: Cross-linking process is performed using high energy such as heating, radiation exposure, electron beam radiation or light irradiation, using a peroxide compound as cross-linking reaction initiator.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The precursor of acid/acid-salt group is coupled to fluoro ether side chain, and is of formula: -O-(CF2CFY1-O)n-(CFY2)m.Y1=fluorine atom, chlorine atom or perfluoro alkyl group, preferably trifluoro methyl;n=0-3, preferably 0 or 1;m=1-5, preferably 2;Y2=fluorine atom or chlorine atom, preferably fluorine atom.The ether bond of fluoro ether side chain is carried out to the carbon atom which comprises the perfluoro ethylene unit in principal chain of crosslinkable fluorine-containing polymer. Preferred Composition: The fluorine containing polymer liquid composition further contains a fluorine containing polymer liquid (A), a crosslinking agent (B) of formula (III), alcohol (C) chosen from methanol, ethanol, propanol and/or tetrafluoro propanol, filming adjuvant (D) such as organic liquid of boiling point 100-300degreesC, and active substance (E).R19,R20=-NH2, -NH-Ph, -OH or SH, preferably -NH2;Ph=phenyl group;andR21=-SO2-O-, -CO-, 1-6C alkylene group, 1-10C perfluoro alkylene group, or single-bond.The cross-linking agent (B) is polyfunctional unsaturated compound such as triaryl isocyanurate. The filming adjuvant (D) is phosphoric acid ester, monohydroxyl ether of ethylene oxide oligomer and/or cyclic amide or its derivative.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Substance: The active substance (E) is catalyst, which a metal containing platinum.Preferred Process: Cross-linking process is performed using high energy such as heating, radiation exposure, electron beam radiation or light irradiation, using a peroxide compound as cross-linking reaction initiator.    TECHNOLOGY FOCUS - POLYMERS - Preferred Polymer: The crosslinkable fluorine-containing polymer is obtained from a fluorine containing polymer precursor obtained by polymerizing fluoro vinyl ether derivative of formula: CF2=CF-O-(CF2CFY1-O)n-(CFY2)m-A.Y1,Y2,m,n=as defined above;A=-SO2X, -COOM31/_L, or organic group upon hydrolysis transformed into carboxyl group, such as -COOR12 or -CONR24R25;X=halogen atom,-OM41/_L, -NR13R14, or -ONR15R16R17R18;R13,R14=H, alkali metal, alkyl group or sulfonyl-containing group;M3,M4=L-valent metal;R15-R18=H or 1-4C alkyl group;andR24,R25=alkyl or hydrogen atom.Preferred Components: The fluorine-containing polymer precursor is a copolymer obtained by polymerizing fluoro vinyl ether derivative and fluorine-containing ethylenic monomer. The crosslinkable functional group is cyano group or crosslinkable carboxyl group.Preferred Composition: The solid content concentration of dispersion liquid (AD) is 2-80 mass%. The dispersion liquid (AD) is fluorine-containing polymer aqueous dispersion (ADA) whose liquid dispersion medium is aqueous dispersion medium having water content of 10-100 mass%. EXAMPLE - Perfluoro cyclobutane (in g) (227.5), perfluoro (ethyl vinyl ether) sulfonyl chloride (168.2) and CF2=CFOCF2CF(CF3) OCF2CF2CN (16.l) were deaerated. Tetrafluoroethylene was added and stirred at 30degreesC.8 mass% perfluorohexane solution of di(~o-hydroperfluoro hexanoyl) peroxide (3.56) was added and polymerized. Unreacted tetrafluoroethylene was removed and chloroform (250 ml) was added and stirred for 30 minutes. The reaction mixture was solid liquid separated, and chloroform (250 ml) was added to the solid content and stirred for 30 minutes. The obtained polymer was washed and chloroform was removed. A copolymer (21.8) having perfluoro (ethyl vinyl ether) sulfonyl fluoride (16.2 mol%) was obtained. Fluorine group solvent (H(CF2)4Cl) (400 ml) was added and maintained at 150degreesC for 12 hours. 2,2-bis(3-amino-4-(N-phenyl amino) phenyl)hexafluoro propane (32 mg) was added, and the obtained solution was impregnated into polytetrafluoroethylene porous film and dried for 30 minutes at 80-100degreesC. The obtained coating film was baked at 200degreesC for 10 minutes and immersed into pure water and the thin film was peeled from the glass panel. The obtained thin film had thickness of 15 microns, and excellent durability.