NOVELTY - The method comprises dissolving polyvinyl alcohol PVA1788 in de-ionized water at 90-95 degrees C, cooling to 20-24 degrees C, adding n-butanal and mixing uniformly, where the mass ratio of alcohol and n-butanal is 1:0.50-0.55 and the mass ratio of alcohol and water is 3:47-50, dropwise adding hydrochloric acid (15-20%) for 8-14 minutes and stirring at 20-24 degrees C at a stirring speed of 110-140 circles/minute, where the mass ratio of alcohol and hydrochloric acid is 1:0.74-1, stirring for 5-8 hours at the constant temperature of 20-24 degrees C, and raising the temperature to 45-55 degrees C.    USE - The method is useful for producing high-elastic polyvinyl butyral, which is useful as a high-elastic polyvinyl butyral membrane piece (claimed) for preparing safety glass for building, front windshield for automobiles and solar battery board interlayer film.    ADVANTAGE - The method is capable of effectively producing the polyvinyl butyral with high elasticity and improved impact resistance, soundproof effect, heat resistance and radiation resistance.    DETAILED DESCRIPTION - The method comprises dissolving polyvinyl alcohol PVA1788 in de-ionized water at 90-95 degrees C, cooling to 20-24 degrees C, adding n-butanal and mixing uniformly, where the mass ratio of alcohol and n-butanal is 1:0.50-0.55 and the mass ratio of alcohol and water is 3:47-50, dropwise adding hydrochloric acid (15-20%) for 8-14 minutes and stirring at 20-24 degrees C at a stirring speed of 110-140 circles/minute, where the mass ratio of alcohol and hydrochloric acid is 1:0.74-1, stirring for 5-8 hours at the constant temperature of 20-24 degrees C, raising the temperature to 45-55 degrees C and continuing stirring for 4-6 hours at a stirring speed of 75-90 circles/minute, cooling the reactant to room temperature, filtering and water-washing until the filter fluid becomes neutral, immersing it by sodium hydroxide solution (15-20%) for 10-15 minutes, water-washing and drying at 45-60 degrees C, and obtaining polyvinyl butyral. An INDEPENDENT CLAIM is included for a high-elastic polyvinyl butyral.