Water has fascinating properties in its supercritical state where it behaves very differently from water at standard conditions. Supercritical water has many particularities, such as intensive oxidation, extraordinary solvating power, and the density of supercritical water varying between gaslike and liquidlike values by varying its pressure and temperature. Almost all hydrogen bonding of water is broken down at the supercritical temperature of 400℃. This nature of supercritical water is probably the main reason that it has many particularities.Water in mantle not only has an important influence on the nature of geophysical fields, but also has an important connotation on the evolution of geological structure, geochemical dynamics, mineralization, and discussion about the reason of deep geological calamity (earthquake and volcanic eruption). The existence of water and other liquids is likely an important reason which the earth has different evolutionary history from other planets. Therefore, study on the interaction between water and deep Earth's materials becomes an important content of understanding the evolutionary process of the deep Earth and the whole Earth.