The present invention relates to a polymer blend electrolyte membrane comprising an inorganic polymer having polydimethylsiloxane as a main chain, which has a pore structure at both ends formed by condensation reaction between 3-aminopropyltriethoxysilane and tetraethylorthosilicate, wherein phosphoric acid is chemically linked to an amino group of the pore structure; and a proton-conducting polymer having a cation exchange group at the side chain thereof, as well as a manufacturing method thereof. Generally, proton-conducting electrolyte membranes have significantly reduced ion conductivity at high temperatures. However, proton-conducting electrolyte membranes have advantages in terms of efficiency and cost, and thus it is needed to develop an electrolyte membrane, which has excellent ion conductivity even at high temperature. Accordingly, the present invention aims to provide a polymer blend electrolyte membrane for use at high temperature and a manufacturing method thereof.