Abstract: In the deep mining activities, the surrounding rock enters the post-peak stage after being disturbed by the project, and its mechanical properties are quite different from those before the peak. It is important to investigate the stress and strain response characteristics of the post-peak unloading confining pressure for roadway support. Based on MTS815 equipment system, a confining pressure test of unloaded sandstone with fixed axial strain after peak under different confining pressures was carried out. The influence of mechanical properties of sandstone during confining pressure relief is discussed. The research result showed that with the increasing of confining pressure, peak strength and post-peak strength are both conform to line Mohr-Coulomb strength criterion in experiment. The shear ratio K decreases with the increasing of axial stress during pre-peak, but the rate of change slows down gradually and reaches the minimum value 0 at the peak strength; after the peak of axial stress, K value gradually increases and remains unchanged at the residual strength stage.