Abstract: D net work numerical modeling technique for discontinuities of rock mass is a new technique developed recently, which can be a very important basic work to evaluate the stability and geometric parameters for engineering design in jointed rock mass. The technique is based on the in situ investigation of discontinuity traces in sampling window, with the application of probabilistic statistics, stochastic, mont carlo simulation and computer programming, to correct the bias of orientation, trace, spacing from sampling window,and finally,3 D net work numerical model for discontinuities is formed.