Abstract: To investigate the damage and permeability characteristics of rock under unloading confining pressure conditions,a numerical simulation of a triaxial unloading permeability test was conducted using the particle flow discrete element software PFC^2D. The study focused on the acoustic emission(AE)characteristics,microcrack and damage evolution,force chain distribution,coordination number variations,and energy conversion and dissipation features of sandstone samples at the mesoscopic scale during monotonic loading,constant axial pressure unloading,and stress drop phases,for various initial confining pressures. Additionally,the relationships between stress and permeability evolution,as well as the characteristics of cracks and permeability,were explored. The simulation results indicated that AE signals emitted by the sample during loading and unloading can be classified into four distinct stages: quiescence,stability,burst,and decline. The number of cracks at the point of failure in the sandstone samples increased with higher initial confining pressures. During the loading phase,changes in the force chain distribution within the specimen led to the formation of stress concentration zones. As the initial confining pressure increased,so did the degree of stress concentration,which intensified crack development and resulted in a greater number of "voids" within the contact force chains. Furthermore,the total input energy,elastic strain energy,and dissipated energy at the time of failure all increased with the rise in initial confining pressure. Permeability of the sample increased with the formation of cracks,exhibiting a three-stage pattern: an initial decrease,followed by a period of slow growth,and finally a rapid increase. Higher initial confining pressures made it more difficult for permeability to develop. Macroscopic fracturing caused an overall increase in sample permeability,with seepage transitioning from "pore flow" to"fracture flow."This research provides valuable insights into the mechanisms of rock damage and permeability evolution under unloading conditions and offers essential theoretical support for engineering construction and disaster prevention in environments characterized by high geostress and hydromechanical coupling.