The thermopower of decagonal AlCuCo quasicrystal was measured in the periodic and quasiperiodic direction by laser heating alternating current measurement method in the temperature range of from 300 K to 1200 K. We found that the thermopower is negative in the periodic direction and positive in the quasiperiodic direction. The thermopower hopps at 1123 K （850 ℃） along the periodic direction. The change of the thermopower is not monotonic at high temperature. The measurement method we used is sensitive to the phase transition point.