Abstract: First of all, the significant historic position of van der Waals equation is commented. Using van der Waals molecular model for gas-liquid states, the deviation of two ideal gas laws, the characteristics of gas-liquid transition and the theorem of corresponding state are analysed premarily. Liquefaction of gas and low temperature techniques are presented briefly and the significance in low temperature physics and theory of phase transition are emphasized.

Key words: van der Waals state equation, Boyle＇ s law, Joule-Thomson effect, gas-liquid transition., theorem of corresponding state, low temperature technique