Asymmetric, anisotropy, irregular, discontinuity is the basic properties of rock mass due to the fractures extensive universal developed, that gives rise to complicated physical and mechanical behavior of rock mass, strength of rock mass is influenced by size effect, representative elementary volumes (RVE) has a very close relationship with the size effect of the rock mass, RVE value is calculated in different direction, the result shows that the RVE also has the anisotropic characteristics. Field observation value of fractures is obtained by the method of sampling windows during the field geological survey, then, the statistical homogenous zones is demarcated based on Miller’s method, the bias of observed trace length, orientation and spacing of fractures is corrected in each homogenous unit, and then a three dimensional fracture network models for different homogenous unit are established by using Monte-Carlo method. The REV of rock mass is calculated based on the three-dimensional fracture network. Based on the 3D fracture network model, the volume fracture intensity index (P32) and multisampling non-parametric statistical test method are used to analyze the REV characteristics in different sampling directions. With the increase of the number of fracture groups, the anisotropic characteristics of REV become more obvious. Acknowledgments This work was supported by the State key program of National Natural Science Fund of China-Yunnan Joint Fund (Grant No. U1702241).