The thermoelectric power of copper at high temperature is calculated by a realistic model. The Fermi vector, Fermi velocity and wave functions are determined by APW. The phonon spectrum is calculated by the Born-von Karman atomic-force-constant model. The matrix elements of the electron-phonon interaction are given by the single site approximation. It is found that the calculated value of the thermoelectric power has a positive sign and its magnitude is roughly equal to the observed one.