By carrying out triaxial unloading test under different stress paths on rock

the complete stress-strain curves

deformation characteristics and its strength criterion are studied. The test results show that the relation between lateral strain and confining pressure firstly is linear

and then is nonlinear in the total stage of unloading confining pressure. And its growth rate is about 3 to 5 times the growth rate of the axial strain. It shows obvious lateral dilatancy

and the degree of dilatancy is related to the unloading path. According to the area that is enclosed by confining pressure and volumetric strain curve

it can be seen that the greater the confining pressure is before unloading

the more the energy releases. Deformation modulus decreases gradually with the unloading confining pressure

and increases with the initial confining pressure; the relation between deformation modulus and confining pressure shows negative exponential distribution overall. At the same unloading paths

the reduction of the deformation modulus increases with the increase of initial confining pressure. The Poisson′s ratio rises up continually

and the variation law with the confining pressure can be well described by nonlinear. Failure characteristics of rock are mainly shear failure. The strength characteristics of rock can be well characterized by using the Mohr strength criterion of power function. These conclusions provide reliable theoretical reference and guiding significance for the deep mining of the underground metal mine.