The present invention relates to a branched and sulphonated multi block copolymer and an electrolyte membrane using the same, more precisely, a branched and sulphonated multi block copolymer composed of the repeating unit represented by formula 1 and a preparation method thereof, a hydrogenated branched and sulphonated multi block copolymer, a branched and sulphonated multi block copolymer electrolyte membrane and a fuel cell to which the branched and sulphonated multi block copolymer electrolyte membrane is applied. The electrolyte membrane of the present invention has high proton conductivity and excellent mechanical properties as well as chemical stability, so it can be effectively used for the production of thin film without the decrease of membrane properties according to the increase of sulfonic acid group since it enables the regulation of the distribution, the location and the number of sulfonic acid group in polymer backbone.