Abstract: The gas in the pressure vessel during discharging expands and works to the environment,and its temperature falls to cause the drop of the temperature of the pressure vessel.This paper proposes a simplified cylinder model by taking the discharging of a oxygen tank in winter as an example.The factors contributing to the temperature drop and the temperature drop range during the discharging of the pressure vessel is studied by the theoretic analysis and numerical calculation,and the optimization design for this condition and the lowest allowable operation temperature to avoid the low temperature condition are given..