Abstract: Brittle rock mass generally reserves high strain energy under high ground stress condition.As it is excavated,rock burst will take place with a rapid release of reserved energy.This paper explores the mechanism of rock burst and obtained the following points: (1) Phenomena have shown that rock burst is possibly a kind of tensile and tension-shear failure and the failure angle is relatively small.It is pointed out that excavation can induce tensional stress state in rock mass.(2) Two and three dimensional criterions for rock burst based on Griffith theory have been proposed,and the theoretical analysis has confirmed that the failure angle will be reduced with the occurrence of tensional stress state,till zero while pure tensional state. (3) The energy analysis has shown that the energy consumed for pure tensional failure is relatively less than that for tension-shear failure or compressive-shear failure.And the strain energy dissipated in failure will mainly transferred into surface energy for newly created cracks and the kinetic energy of the failure pieces of rock.Theoretical analysis has proved that the proportion of kinetic energy is much bigger than that for surface energy. (4) The probable applications of this theory include: predicts the failure mode,location and size of rock burst; and theoretical basis of stress control for excavation design.