Using density functional theory (DFT), the reaction of chlorine trifluoride oxide with water was studied. At the B3PW91/6-31++G(d, p) level of DFT, the geometries of reactants, transition states, and products were optimized and the vibration frequencies and zero point vibrational energies (ZPVE) were calculated. Their energies were obtained with the correction of ZPVE. Results show that the energy barriers of the reaction of chlorine trifluoride oxide and water are very low, and a plenty of water is in favor of producing HF, HClO₂ and HClO₄, however, insufficient water is in favor of producing HF and ClFO₂.