Abstract:he probability distribution model of discontinuities is established through the three-dimensional network modeling based on real joint distribution accessed geological survey in-situ. The fracture network coupled seepage model based on interface stress element can be founded by the use of hydraulic parameters and geometry parameters to characterize space structure infiltration layout in rock mass,which can access rock network fractured seepage path,and also it can calculate the water heat distribution,then it can search out all limited block in the exposed surface sections and determine its space geometry and geometric parameters,to achieve to search automatically the instability key block. All of these are of great significance to evaluate and predict the stability of the key block.