A sulfonated polyphosphazene copolymer proton exchange membrane material, and a method for preparing such membrane includes a macromolecule initiator as bromo polyphosphazene is subjected to atom transfer radical polymerization with styrene, yielding a graft copolymer, which is hydrazinolyzed with hydrazine hydrate resulting in a copolymer including a hydroxyl group. The copolymer is reacted with 1,4-butane sultone to yield a sulfonated copolymer finally. The polymer is cross-linked with 2,6-di(hydroxymethyl)-4-methyl phenol (BHMP) as a cross linking agent in the presence of methyl sulfonic acid, yielding cross-linked proton exchange membrane. Such cross-linked graft copolymer membrane has high proton conductivity, low methanol hindrance, and low cost, and has ideal effect when applied in fuel cells as proton exchange membrane material.