The stability of large underground caverns in high geostress area has always been the hot topics of many rock mechanics professors’ attention. Based on the happening mechanism of opening displacements and considering the theory of energy dissipation

this paper makes a preliminary study of the constitutive equation of brittle rockmass in high geostress zone and their engineering application. First

a variational-modulus model has been received during the unloading course from the point of energy dissipation and this aspect is considered in the constitutive equation. Dissipation of energy can be gained from the theory of crack growth. Second

taking advantage of FLAC3D

we compile the above constitutive equation model on the Microsoft Visual C++ environment

and realize the secondary further development of FLAC3D. Third

the stability of surrounding rock and the excavation step in the large underground caverns of Jinping hydropower station are simulated by the developed program. The results indicate that this variational-modulus model is closer to real excavation. It offers some instructions to similar projects.