Abstract: To address the issues of surface subsidence and surrounding rock instability caused by the use of saturated waste rock for filling in goafs of a copper mine，the safety and applicability of the filling technology under water immersion conditions were evaluated to provide a basis for mine disaster preven⁃ tion. Based on the actual working conditions of a copper mine，a comprehensive approach using mechani⁃ cal tests，numerical simulations，and theoretical analysis was employed to systematically investigate the mechanical characteristics of the filling and their influence mechanisms on the stability of the surrounding rock. Firstly，through uniaxial compression and splitting tests，the basic mechanical parameters of the ore body，surrounding rock，and saturated waste rock filling body were determined. Combined with the Hoek�Brown criterion，the rock strength was reduced for engineering purposes，and a 3D numerical model re⁃ flecting the geological conditions was constructed. Secondly，based on the actual excavation sequence of the mining area，a four-stage numerical simulation scheme was designed to dynamically reproduce the en⁃ tire process of void formation，filling，and water immersion in the void area，and to quantitatively analyze the evolution laws of surface subsidence，horizontal displacement，and the distribution characteristics of the surrounding rock stress field. The research results show that the filling operation significantly inhibited surface deformation. The maximum subsidence is 265.84 mm，and the horizontal displacement is within 0~ 30 cm. The overall deformation meets the standards of grade I~II surface protection. However，long-term saturation of the filling body leads to strength deterioration，triggering secondary disaster risks. Significant stress concentration phenomena occurs in the pillar and roof areas，with the maximum principal stress reaching 53.48 MPa. The depth of the local plastic zone expansion increases，forming potential shear slip planes. Through multi-method coupling analysis methods，the stability of the filling mining area under complex hydrogeological conditions can be accurately evaluated. The research results provide theoretical support and technical references for the rational selection of filling processes and the establishment of di⁃ saster warning thresholds in similar mines，and have certain practical value for achieving green and safe mining in mines.

Key words: goaf , saturated waste rock filling body, numerical simulation, ground subsidence