Freeze-thaw cycles is an important factor affecting rock landslides in high-altitude mountainous areas. Granite samples from high-altitude mountainous areas is collected and triaxial unloading tests on granite with prefabricated cracks under different freeze-thaw cycles are conducted. The quality changes, mechanical properties, energy evolution laws, and acoustic emission characteristics of granite is analyzed, and the macro and micro failure modes of granite with prefabricated cracks are revealed. The results show that the rock mass loss rate increases exponentially with the increase of the freeze-thaw cycles, while the rate of change of the rock mass loss rate increases faster. The increase of the freeze-thaw cycles will weaken the strength of the rock samples by exacerbating the internal damage of the rock and increasing the number of the initial fissures, and the existence of the prefabricated fissures weakens the strength of the rock samples while the increase of the circumferential pressure can increase the strength of the rock samples. In addition, freeze-thaw cycles will obviously reduce the strength of the granite. The cohesion of no-fissure, 2cm-fissure and 4cm-fissure rock samples decreased by 17.16%, 50.07% and 74.71% respectively after 60 cycles. With the growth of prefabricated fissures, both absorbed energy and dissipated energy by granite in the process of destruction showed a decreasing trend. Compared with the rock samples with no prefabricated fissures, the total energy, the elastic energy and the dissipated energy of the 2cm-fissure granite at the peak strength decreased by 28.0%, 25.7%, and 35.0%, respectively. With the increase of freeze-thaw cycles, the failure modes of the specimen were changed from tensile failure to shear failure. The shear process of granite was divided into four stages, and the maximum values of AF and RA increased with the increase of the stage number. Using the b-value for prediction, it was found that there is a systematic decrease in the b-value before the rock is damaged by compression, with the b-value decreasing by 63.1%, 64.1%, 92.9%, and 88.5% under each cycle, respectively. Finally, the body porosity and fractal dimension of rock samples were analyzed by CT scanning and fractal dimension, both of which increased significantly with the freeze-thaw cycles. The freeze-thaw cycles caused more obvious damage to the rock samples with prefabricated fissures, especially the cracks around the prefabricated fissures developed intensively.