In view of the problem that the thickness of cryogenic plate is beyond the allowable range for a high pressure and low temperature pressure vessel in a gas field at South China Sea, measures are proposed to reduce the wall thickness of the cryogenic pressure vessel by reducing the design pressure, reducing the diameter of the cylinder and reasonably combining the design conditions of pressure and temperature. The method of material selection for the pressure vessel under high pressure and low temperature is obtained, which can be used for the reference of the design of pressure vessel with large wall thickness at high pressure and low temperature.