NOVELTY - Sulfonated polyaryletherketone is dissolved in solvent, to obtain solution (A). Inert gas is supplied into solution (A), and then reductant e.g. zinc powder is slowly added. Product is filtered, filtrate is condensed and dried, to obtain reduzate. Obtained product is dissolved in solvent, to obtain solution (B) which is subjected to reduction, to obtain modified sulfonated polyaryletherketone. Solvent is acetone, methanol, ethanol, water, acetonitrile, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, diphenylsulfone, sulfolane and/or N-methyl pyrrolidone.    USE - Modification of sulfonated polyaryletherketone used for preparing polymer electrolyte material (claimed) for direct methanol fuel cell (DMFC), polymer electrolyte membrane fuel cell (PEMFC), ion exchange resin, film separator and sensor.    ADVANTAGE - The method provides modified sulfonated polyaryletherketone using simple processes. The polymer electrolyte material prepared using modified sulfonated polyaryletherketone has high mechanical strength, electroconductivity, alcohol-resistant property and size stability.    DETAILED DESCRIPTION - Sulfonated polyaryletherketone is dissolved in solvent, to obtain 3-25% solution. Inert gas is supplied into solution, stirred, then reductant is slowly added to mixture at 10-50 degrees C and reacted at 30-150 degrees C for 3-24 hours. The ratio of sulfonated polyaryletherketone and reductant is 120:1-40. The obtained product is filtered, filtrate is condensed and dried in vacuum, to obtain reduzate. The obtained product is dissolved in solvent, to obtain 5-20% solution which is then reduced, to obtain modified sulfonated polyaryletherketone. The solvent is chosen from acetone, methanol, ethanol, water, acetonitrile, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, diphenylsulfone, sulfolane and N-methyl pyrrolidone. The reductant is chosen form zinc powder, magnesium powder, reduced iron powder/hydrochloric acid, tin dichloride/hydrochloric acid, lithium aluminum hydride, sodium borohydride and palladium/carbon/hydrazine hydrate. An INDEPENDENT CLAIM is included for preparation of polymer electrolyte material using modified sulfonated polyaryletherketone. The modified sulfonated polyaryletherketone is mixed with crosslinking agent under protection of inert gas, temperature is controlled to 0-50 degrees C and stirred for 0.5-8 hours, to obtain filming solution. The ratio of sulfonated polyaryletherketone, catalyst and crosslinking agent is 100:(0-40):(0-50). The filming solution is coated on substrate to form film, solvent is removed by warming at 40-180 degrees C, cooled to room temperature and then defilmed. The product is soaked in dilute sulfuric acid solution for 24 hours, repeatedly washed using water and dried, to obtain crosslinked polymer electrolyte film material. The crosslinking agent is polyaldehyde or polybasic carboxylic acid. The catalyst is acid catalyst or basic catalyst.