Abstract: To solve the surrounding rock instability induced by high in-situ stress in deep metal mines，taking the -450~-540 m sublevel of a skarn-type iron mine as the engineering background，an op⁃ timization study on ore chamber span is conducted targeting the problems of unreasonable stope parameters and poor mining stability existing in the sublevel open stoping with backfilling method. A fixed-beam me⁃ chanical model of the roof is established by the cusp catastrophe theory，and the theoretical ultimate span of the roof is calculated to be 17.24 m，based on which three preliminary span schemes of 12 m，15 m and 18 m are selected. Numerical simulation is carried out with FLAC3D ，rock mass parameters are converted based on the Hoek-Brown criterion，and the Mohr-Coulomb criterion is adopted to compare and analyze the surrounding rock stability. The results show that the ore chamber span presents a non-linear positive cor⁃ relation with roof subsidence and tensile stress. The roof subsidence of 12 m and 15 m spans is 29.00 mm and 36.68 mm respectively，with good stability. The subsidence of 18 m span reaches 52.30 mm，and the plastic zone area is 115% larger than that of 12 m span，indicating progressive failure of surrounding rock. Considering both safety and production efficiency，the optimal ore chamber span is determined as 15 m. The research method integrating theoretical analysis with numerical simulation can provide reference for stope structure design and surrounding rock control in similar deep mines.

Key words: cusp catastrophe theory, sublevel open stoping with backfilling method, stope structural parameters, numerical simulation, deep mining, surrounding rock stability