The resistance and thermoelectric power were measured for a series of single phase YBa2 Cu3O7-x samples with different quenching temperature. The relation between the thermopower and temperature indicates that there exists a phonon-drag peak in orthorhombic phase sample. The peak disappears in tetragonal phase sample. This phenomeron suggests that the electron-phonon interaction influences the superconduc tivity of YBa2 Cu3O7-x. According to the experimental data of thermoelectric power, estimation for the Fermi energy and carrier concentration of the sample are made.