Abstract: According to the results of slate triaxial compression tests under different confining pressures, slate's failure and energy variation under different confining pressures are analyzed. The results show that elastic energy and dissipation energy have different change situation when slate is at different deformation stages. The elastic energy increases firstly and then decreases, dissipation energy at the beginning of loading is almost zero, increases rapidly at yield stage. Considering the ratio of elastic energy and the total energy absorbed, development of fracture is divided into three stages in the process of compression:steady development stage, accelerated development stage and connecting stage. Linear formula of rock samples are obtained by fitting the total absorbed energy, dissipation energy and confining pressure. When loading to yield strength stage, U^e' is almost equal to U^e; When loading to peak strength stage, U^e' is less than U^e, and the difference is growing. By defining damage variable from the view of energy, we can draw conclusions that low confining pressure state corresponds to low energy dissipation and high damage variable; otherwise, high confining pressure state corresponds to high energy dissipation and low damage variable.