To identify the hydrolysis characteristics of PET the decomposition rate and yield for conversion from PET into products were compared by varying reaction temperature, pressure and time in the range of the subcritical and supercritical water. Experiments were conducted by the batch bomb reactors using the molten salt bath with temperature ranging 300 to 400 ℃ and pressure ranging 15 to 40 MPa and reaction time ranging 1 to 30 min, and then the product distribution by the reaction variables was investigated. The main product of reaction was its monomer, terephthalic acid(TPA). But little gaseous products were formed in these reactions. Decompositions of PET and yields of TPA were increased with increasing pressure and reaction time at each temperature. Maximum yields of hydrolysis products and PET decomposition at pressure of 30 MPa were 85.33% and 83.55% at 300 ℃ in the subcritical region and 94.45% and 95.45% at 350 ℃ with 30 min of reaction time in the near-critical region which 98.25% and 98.24% at 400 ℃, with 8 min of reaction time in the supercritical region respectively. Therefore PET could be successfully decomposed at a very short reaction time under supercritical water condition. The PET hydrolysis reaction was reversible second order and the activation energy was 144kJ/mol under 30 MPa and 350 ℃.