Abstract: More and more large underground power houses are under the geological environment of large buried depth, high ground stress and high pore water pressure. At the same time, it is complicated to analyze the stability of underground houses because of the existence of joints in the rock mass. The joints make intension of the rock mass decrease. According to these characteristics, a new visco-elastoplastic mechanical model is deduced. The model has a comprehensive consideration of damage and rheology. Besides, regarding VC++ as the plat form, the secondary development function of FLAC3D is employed to make a program of this constitutive equation. It is a dynamic link library (DLL) and can be used by the main program of FLAC3D. A new damage rheology FLAC3D rock mass is developed. In the project of Shuangjiangkou large underground power houses, the program model for joins is used to analyze the ability of houses and to guide the design of engineering. The results show that it is quite strong feasible to use this new damage rheology FLAC3d model to simulate the excavation of large underground power houses and analyze the stability. The analytic results can be used to guide the construction of engineering.