In order to explore the mechanical characteristics of confined-pressure soaking (CPS) sandstone during the damage-fracture process, the uniaxial compression and acoustic emission (AE) experiment of CPS sandstone was conducted. The mechanical parameters, fracture morphology, AE and energy characteristics under uniaxial stress were researched. The results show that the uniaxial compressive strength and elastic modulus decrease as a logarithmic function with CPS parameters, corresponding to the inflection point of modification. The fracture mode gradually changes from brittleness to toughness with the increase in moisture content. The difference between fracture fragmentation and mechanical behavior mainly depends on the degree of CPS. The evolution of AE characteristics and energy dissipation has a good correspondence with CPS specimens. The higher the CPS degree is, the less the AE cumulative number is and the longer the excitation time is. Based on the phase variation of AE events and energy dissipation, the CPS damage variables are proposed to quantify the weakening degree and reveal the damage evolution process. The results provide a useful foundation for evaluating rock failure and improving service life.