Abstract: In this paper the mining effect caused by undergroud mining and deformation characteristics of the land subsidence basin are evaluated by using numerical simulation method. The maximum land subsidence caused by the first-term excavation is less than 700 mm, the maximum subsidence caused by the second-term deep excavation will not be larger than 995mm. If back-filling in the stopes is used, the maximum subsidence will be reduced by 55%. Because the relative defferential subsidence deformation of the land surface is less than 1mm. m-1, and there exist two overlying impermeable clay layers (thickness from 3～5 m to 5～7 m, respectively), such deformation of the land surface will not destroy the continuity of clay layers and not provide any path for surface water (seawater) to harm the safety of the mine.