Abstract: Rock is a heterogeneous and anisotropic natural medium composed of randomly distributed grains and fractures. Combined with the uniaxial cyclic loading and unloading test of red sandstone,the composition of strain energy density during loading and unloading is redefined,including plastic strain energy density and elastic strain energy density. And the latter is the sum of fracture strain energy density and base-material strain energy density. The aim is to further explore the energy evolution characteristics of red sandstone under cyclic load. Studies indicate that: ① With the increase of stress level,the strain energy increases exponentially. And the elastic strain energy dominates,60%-80%,where in the base-material strain energy is not less than 70%. In the plastic stage,their growth rates decrease;② The whole loading and unloading process is divided into three stress level stages:lower than 20% stress level,20%-70% stress level and more than 70% stress level,which is consistent with the rock compaction stage,elastic stage and plastic stage;③ The elastic energy index increases first and then decreases,and the maximum stress level is about 65%-75%. Under this stress state,the possibility of rockburst initiation is increased. And the rebound deformation index generally shows the trend of decreasing,fluctuating,rising and decreasing,reflecting the deformation characteristics of rock internal base material and fracture. The research results can be used as the theoretical basis for analyzing the stability and rockburst risk of engineering rock mass.