Abstract: According to the subsidence caused by “three-under ” mining disturbance，combined with the full tailings cemented material test，FLAC^3D is adopted to comprehensively analyze the surface subsidence and deformation caused by different strength of filling body in the backfill process of an iron-zinc mine.According to the mining rock mechanics parameters and the related experimental results，the settlement and deformation under different strength of the filling body are respectively simulated，and then the simulation results are optimized according to relevant criterion.It is determined that the strength of the filling body 0.8 MPa can guarantee the normal operation of the highway and the river with the surface settlement，and meanwhile ensure the smooth mining.

Key words: Surface subsidence, Three-under mining, FLAC3D, Strength