Abstract: The mining of ore bodies under the thick Quaternary aquifer has the problems of instabili⁃ ty of surrounding rock，sudden change of mining seepage and high risk of water inrush. The coordinated control of mechanical stability and hydrological safety is the core of safe mining of such ore bodies. Taking the ore body above-220 m level of an iron mine in Anhui Province as the engineering background，the opti⁃ mization of stope structure parameters was studied by combining theoretical analysis with numerical simula⁃ tion. Based on the thick plate theory，combined with the geological conditions of the mining area and the state of seepage risk，the multi-level safety factor is set differently，and the design method of the safe thickness of the top pillar suitable for the sublevel open stoping with subsequent filling method is estab⁃ lished. Based on FLAC3D software，a three-dimensional fluid-solid coupling model is constructed to simu⁃ late five stope width conditions of 8，10，12，15 and 18 m，and the evolution laws of surrounding rock stress，displacement，plastic zone，pore water pressure and seepage velocity are systematically analyzed. The results show that 12 m is the critical value of the stope width in the mining area. When the mining width exceeds this value，the roof settlement，surrounding rock stress and seepage velocity increase nonlin⁃ early. The plastic zone of the roof gradually penetrates and forms a potential water channel，and the risk of mechanical and seepage coupling disaster increases significantly. Based on the comprehensive mining safe⁃ ty and production efficiency，the optimal stope structure parameters are determined to be 100 m in length and 12 m in width. The study clarifies the mechanism of mining instability and seepage mutation of ore bod⁃ies under complex hydrogeological conditions，which can provide theoretical support and technical refer⁃ ence for safe and efficient mining of similar mines.

Key words: open stoping with subsequent filling method, fquid-solid coupling, roof stability, stope parameter optimization, FLAC^3D