The stability of underground openings concerns the safety of field personnel and engineering facilities in tunnelling and underground mining. The pre- and post-peak damage characteristics of sandstone subjected to triaxial cyclic loading were experimentally studied. The results show that the maximum dissipated energy occurs after the peak stress. The maximum of energy dissipation ratio K and the stress ratio at the K peak point increased with the confining pressure. To estimate the damage characteristics of rock material, the damage variable D was defined based on rock dissipated energy. It is found that the confining pressure has a negligible influence on the damage variable D rate in the pre-peak stage. However, it increased at a lower rate with the increase of confining pressure in the post-peak stage. It is found that the proposed rock damage variable associated with dissipated energy and confining pressure, is a significant indicator of the overall loss of load-carrying capacity of rock in pre-peak and post-peak stages.