Abstract: The mechanical parameters and the size effect of the jointed rock masses are one of the hotspots and a difficult task in the field of the rock mass research work.It is known that the numerical analysis for rock discontinuity network model has not been published yet and that in Xiaowan Hydro-power Dam Station(in China),there are so many rock joints and their mechanical parameters should be characterized.For this purpose,a numerical analysis is done.After analyzing the eigen-values of the joints distributing function,the discontinuity network modeling is established by the Monte Carlo method.The discontinuity displacement numerical simulation for the network modeling is achieved by elaborating an interface program which is injected into a computer program FLAC3D of geotechnical analysis.According to different rock mass samples,the results of the numerical analysis reveal that the deformation modulus of the unloaded rock masses presents a negative exponential function,whereas,basically,the curve of the strength parameters c,? and the rock mass size give a negative power function.The numerical simulation results correlate well with the inclined plane loading test results and the Hock Brown results.