Abstract: The hysteresis phenomenon related to the coexistence of monoclinic-tetragonal phases of zirconia has been analyzed by a developed cladding oxidation model based on diffusion equations. Main findings are summarized as follows: the model can well simulate the hysteresis phenomenon during cladding transient oxidation; when the heating or cooling rates are high, the hysteresis phenomenon is significant; and the model can give a much better prediction of the hypothetical loss-of-coolant accident（LOCA） oxidation experiments in Oak Ridge National Laboratory（ORNL） than the parabolic rate correlation.