Abstract：The fundamental characteristics of Skempton coefficient have been studied based on the theoretical analyses and laboratory under the undrainage. Some tests have been performed under the different conditions，for instance，different confining pressures and different loading types. The mechanism of Skempton coefficient change has also been investigated. That the compressibility of water cannot be neglected is proposed for the calculation of civil engineering. It is very important for the research of mechanical properties of rock mass and soil mass in the Three Gorges reservoir，and in the construction of dam foundation and embankment.
