Abstract: The different excavation rates of tunnels have obvious effects on the mechanical properties of rock mass. This paper selects widely exposed metamorphic sandstone in the Nu River tectonic me'lange belt to carry out true triaxial unloading tests under different unloading rates. The tests use stress and strain monitoring,acoustic emission monitoring,numerical simulation,and other methods to explore the deformation and failure modes and characteristics of the rock under different unloading rates. The test results indicate that the increase in unloading rate causes the number of tension cracks to continue to increase and the failure mode of the rock to become more complex,with symbiotic morphological characteristics of tension cracks and shear cracks appearing. According to the law of energy evolution,as the unloading rate increases,the proportion of elastic strain energy of the rock mass increases,and the proportion of dissipated energy decreases. The energy used for rock mass destruction under peak stress increases,and the sample failure becomes more severe. The change in acoustic emission energy appears in the unloading stage. High unloading rates produce the smallest damage deformation and less energy damage. In the destruction stage,damage occurs earlier,resulting in more severe damage. Numerical simulation tests show that as the unloading rate increases,the rock mass gradually transitions from shear failure to tension failure,and the elastic strain energy and dissipation energy are consistent with the indoor test rules. The faster the unloading rate,the more complex the rock failure becomes.