Abstract：Connectivity rate of discontinuities in rock mass is an important parameter as a reflection of the joints¢ extendible extent and connectivity status，which is also a key factor of estimating the shear strength parameters of fractured rock mass，as well as the precondition of rock slope stability. A calculating method for three-dimensional connectivity rate of rock mass discontinuities has been presented based on 3D network simulation，and its application to shear strength parameters estimation is also discussed. A new technique to estimate the mean trace length in sampling windows by considering the general probabilistic distribution of trace length and obvious decline of discontinuities is suggested using probability statistic method. The estimated mean trace length has been used to construct 3D discontinuous network model of rock mass from the entrance of the diversion tunnel of Yujianhe Hydraulic Project in Guiyang Province. The precision of the model is improved. Based on the constructed 3D network model，the values of 3D connectivity rate in different cross-sections have been figured out by slice method and then they are used to estimate the shear strength parameters of the simulated rock mass through weighted average method. The results show that the anisotropy of rocks in this area is quite obvious and the connectivity is well-developed. The planes with tendency of 70°–80°and inclination angle of 20°–40° are dangerous cross sections，in which the maximum connectivity rate is 0.914 3 and the minimum cohesion and internal friction angle are 1.135 MPa and 25.7° respectively，therefore，more attentions should be paid to engineering construction.
