Abstract: To study the strength characteristics and mechanical parameter evolution of brittle hard rock under high stress loading and unloading cycles, a series of cyclic loading and unloading tests on black sandstone with different confining pressure levels were carried out. The stress-strain curves and fracture characteristics of the high brittle hard rock during the whole process were obtained. By adopting plastic internal variable to represent the degree of rock damage, the evolution of deformation and strength parameters with damage was studied. The research results were as follows: ① In the cyclic loading and unloading test, the stress-strain curve of black sandstone had a yield platform; the post-peak stress dropped rapidly, and the specimen failure mechanism was mainly sheared. ② From the initial yield to the residual deformation, the elastic modulus of black sandstone first decreased and then increased, and it reached the minimum value when the plastic internal variable was about 0.8~0.85; the Poisson's ratio first increased and then decreased. ③ The cohesion decreased with increasing plastic internal variable at first, and remained stable when approaching the residual strength; the internal friction angle first increased and then decreased. The relationship between the strength parameters and the plastic internal variable can be expressed by linear piecewise function.