Abstract: In order to maximize the exploitation of underground ore body and ensure the safety of surface structures on ground，based on a mining engineering example of gentle inclined polymetallic deposit with open-stope method，a three-dimensional model was established with the FLAC3D and the rules of surface subsidence were simulated with the TECPLOT.Eventually，the curve chart of surface settlement was plotted in accordance with the simulated results.The results showed that the subsidence contour line basically follows the sinking form.The surface depression above mined-out area appears maximum and the further away from center is，the smaller subsidence value on the same direction is.The largest surface deposition distance is 120.9 mm，and other surface structures are out of mining damage except for Yangjiacun in dangerous area with the largest settling value of 24 mm.The simulated results of subsidence provide a certain theoretical foundation for exploiting the ore body underground and investigating the incidence with surface structures，which has a crucial practical significance.

Key words: Underground mining, Gentle inclined ore-body, Surface subsidence, FLAC3D, Numerical simulation