Abstract: The faults in the rock strata of the bottom structure of Pulang Copper Mine are crisscrossed. The five faults in the first mining area cut the ore body vertically and horizontally. The ore rock in the fault and the nearby influence zone is broken，the rock self-bearing capacity is poor，and the bottom structure is prone to deformation and failure. Through the long-term follow-up investigation of the site damage，it is concluded that the bottom structure of Pulang Copper Mine belongs to the type of ' strong top and weak side'. Using FLAC3D numerical simulation software，by gradually increasing the vertical stress of the bottom structure，the mechanical state of surrounding rock near the bottom structure fault under different ore accumulation thicknesses is simulated and analyzed. The results show that the displacement and deformation of surrounding rock near the fault are large，the stress state of the bottom structure is related to the distribution of the fault，and the fault has a great influence on the stability of the bottom structure.

Key words: natural caving mining method, bottom structure, fault, stability