We use the magneto-optic imaging to determine the spatial distribution and the time dependence of the magnetic induction B z ( x,t ) on the broad surface of the melt texture growth YBCO bulk. The model-independent effective activation energy U and the current density j could be calculated from B z ( x,t ), ∂ B z ( x,t )/∂ t and ∂ B z ( x,t )/∂ x . The good fit shows that the thermally activated flux creep in the melt texture growth bulk is consistent with the logarithmic model in the temperature range of liquid nitrogen.