The classification as three types is proposed for the load-displacement relation curve of the rock-soil mass at first; a criterion of high earth pressure is defined. A new constitutive theory is at first proposed; the complete-process relation of stress-strain can be described under different normal stresses (or different confining pressures) by this theory. There only exist three mechanical parameters describing the geomaterial and stress state. It describes not only the mechanical behavior of geomaterial

but also of the complex material and of the surface between different media

the arbitrary deformation can be obtained. The relationship of stress-strain for the different rock-soil masses and the surface between rock-soil layer and pile are described by the proposed constitutive theory. The testing data of pile foundation of Changshawan bridge are simulated; the results show: that the mechanical properties of different rock-soil masses and interlayer between rock-soil mass and pile can be presented by this constitutive theory.