Abstract: According to the structure characteristics of joint rock mass in the south slope of Yanqianshan Open Iron Mine in China, a 3-D joint network was simulated and shown by Monte-Carlo random simulation technique. The spatial information of rock mass was visually displayed. Based on the fundamental theory of damage mechanics of rock mass and the 3-D network simulation technique, the probability distributions of random matrix of the damage tensor on joint rock mass were studied. It is shown that the elements of the probability damage tensor matrix obey the normal distribution.