The simulation method of rock mass joint network is studied. The randomness of geometric parameters and mechanical parameters of joint is taken into account in the generated joint network. In order to determine the representative element volume (REV) scale of rock mass

an index is defined by use of the generated joint network. On the basis of the above analysis

the codes for joint network simulating

for network plot outputting and for REV scale analyzing are developed. The rational analysis of the research results and codes is carried out through a case study. The results of a case study show that the REV scale is about three to four times of the maximum expected value of trace length of rock mass joints sets. The research results offer a basis of computation of rock mass equivalent mechanical parameters.