A nonlinear strength criterion for rock- like materials is developed in this paper. Taking α as an angle of micro- failure orientation in rock- like materials, a formulation between α and load is derived from a mixed- mode fracture criterion based on linear elastic fracture mechanics. According to micro- failure experimental phenomena of rock- like materials, a failure characteristic parameter under triaxial compression condition is chosen, which is relevant to confining pressure and is an invariant. A theoretical nonlinear strength criterion is also derived, which is exactly in the same mathematical form as the original Hoek- Brown empirical strength criterion. In addition, it is also found that the coefficient m in the Hoek- Brown criterion has physical meaning which is related to the ratio between the uniaxial compressive strength and the uniaxial tensile strength.