Abstract: Unloading confining pressure tests are conducted before different pre-peak confining pressure of gneissic granite obtained at the foundation of Xiaowan hydrodynamic station,the results show that the deformation modulus changes little,but poisson’s ratio increases greatly compared with the loading conditions under the same confining pressure.Samples with different sizes will show different behaviors under the same unloading confining pressure,and the sample with a larger size will show tensile fa...