Study failure characteristic of rocks under unloading confining pressure conditions from the released elastic strain energy is of great significance.Firstly,unloading confining pressure test maintaining constant axial deformation was carried out by using MTS815 electric hydraulic servo control tester.Secondly,the sandstone deformation,strength,elastic modulus,and energy variation during unloading confining pressure were analyzed by according to unloading confining pressure test data.The results show that with the confining pressure decreases,rock samples occur laterally continuous expansion;modulus of elasticity almost no change in the initial stages and significantly lower after crossed the failure point;axial stress decreases,showing a non-linear characteristic,releasable elastic strain energy increases more slowly in the initial stage,when the confining pressure reduced to a certain extent increases rapidly.Finally,based on the release of elastic strain energy theory deduce the failure criterion of rock unloading confining pressure.The whole failure criterion of loading rock under unloading confining pressure,which was U₀^e,was concluded.