Abstract: According to the theory of Soil-Plant-Atmosphere Continuum (SPAC), water movement in the SPAC system depends on the driving force -water potential gradient (i.e. energy gradient) and flow resistance. However, the essence of present conception of water potential is the difference value of molar Gibbs function of water under isothermal condition, it does not cover the total energy of water in a considered system. A total water potential concept that expresses total energy of moisture in a given system was proposed, and methods for quantifying each component of the total water potential were presented. Finally, the physical meaning and the limitations of the total water potential were discussed to understand some mistake of total water potential application.