Abstract: This is the keynote speech for the 5^th Gu Dezhen Lecture co-sponsored by the Engineering Geology Commission,China Geological Society and the Key Laboratory of Engineering Geomechanics,Chinese Academy of Sciences. The paper briefly recalls the core value and historical contribution of the"Engineering Geomechanics of Rock Masses(EGRM)"founded by Professor Gu Dezhen,and introduces the Statistical Mechanics of Rock Masses(SMRM) and its inheriting and developing to the EGRM in the past 30 years. Referring to the ideology of Statistical Physics,the SMRM has proposed geometric probability models for rock mass structure,the energy principle of fracture mechanics for continuity equivalent of discontinuous rock mass,the principle of structure-stress control to the behavior of rock mass,the principle of weak link control to rock mass strength,and the seepage mechanical principle of discontinuity network. The SMRM has established the constitutive model,the analytical method for complete deformation of rock mass,the model for characteristics and rock burst mechanism of high energy-store rock mass,the analytical solution of circular tunnel in elastic rock mass. The SMRM also has developed the technology and equipment for in situ data acquisition,computational methods for full directional parameters of structure,deformation,compressive strength and shear strength,permeability of rock mass,and anisotropic quality rating and active reinforcement of rock masses,and the module for numerical analysis,i.e. JointModel. The SMRM has strongly promoted the advances of the theory and technology of EGRM and rock mass mechanics.