Abstract: To study the mechanical and acoustic emission characteristics of triaxial unloading of limestone after high temperature, triaxial unloading test in high temperature and acoustic emission monitoring for the limestone were carried out by using MTS815 servo-controlled testing machine. The test results show that: below 400 ℃, temperature has a strengthening effect on limestone; above 400 ℃, temperature has a degradation effect on limestone, acoustic emission count rate also reflects this feature. The temperature can reduce the dilatancy stress level of limestone, after high temperature, as the temperature increases, the dilatancy stress level increases gradually. After high temperature, in addition to 100 ℃, limestone can release energy more easily in the process of external force, releasing energy, and internal crack formation, expansion and penetration is easier in the process of external force.