Abstract：The investigation of the representative elementary volume(REV) of fractured rock mass is a fundamental problem in rock mechanics. Firstly，the general mechanical meaning of REV is discussed by analyzing its definition，and REV is considered as a basic mechanical conception that contains the dialectic relationships of microstructure-macrostructure，discreteness-continuousness，and randomness-determinacy. Then，the close relationship between the REV of fractured rock masses and the choice of mechanical models as well as mechanical parameters is explained. It shows that REV can be regarded as a quantitative criterion for choosing equivalent continuum approach or discrete approach to solve rock engineering problems and it can reflect the size effect of mechanical properties of rock mass. With the summarization of previous studies about REV，the general methodology for investigating the REV of fractured rock mass is presented and the results show that numerical method，based on the modeling techniques of discrete fracture networks，will become a mainstream for estimating the REV of fractured rock masses. Finally，Monte Carlo simulation approach is used to reproduce a two-dimensional rock mass region which contains two sets of random fractures，and the finite element method is adopted to obtain the equivalent elastic modulus of the rock mass under uniaxial loading. According to the variation of equivalent elastic modulus being changed with the size of rock mass，the REV size of the considered. rock mass is estimated to be 9 m×9 m.
