Abstract: A computer simulation method to predict the mechanical properties of jointed rock mass is pre-sented. Starting from the development of a damage-fracture model for jointed rock mass on the basis of the geological investigation of rock joints, the process of in-situ rock mechanical tests is simulated numerically on the computer by using the proposed model. As a result, the anisotropic values of modulus of deformation and shear strength of rock mass are derived from the obtained complete stress-strain curves. Taking as an example, the prediction of mechanical properties for the jointed rock mass of Lax-iwa hydro-power project is described in detail.