Abstract: Prediction of instability and failure of rock mass can provide a basis for the design of rock mass support. The effect of fissure inclination on the energy evolution of rock mass is studied by cyclic loading and unloading. The process of energy evolution revealed the nature of rock deformation and breakage. The study results show that: the elastic energy ratio is about 40%~45% at the beginning of the loading, approximately 55% at the middle stage, and 60%~65% at the later stage; The variation rate of elastic energy ratio has a close relation with the fissure inclination. The energy density increases with the increase of load, and the fissure inclination affects the variation rate of energy density；The more obvious the transition of the ratio of energy density is, the closer the rock mass is to destruction；The increase and decrease of dissipation energy density has a high correlation with the failure process of rock mass；The energy absorption capacity of fractured rock mass increases first and then decreases with the increase of inclination, showing a nonlinear relationship between the fracture angle and the energy evolution. These relations are distinguished in different stages, thus it can be an early indicator to instability and failure of rock mass.