Abstract: Based on the site investigation of geology and analysis of observed deformation, it is shown in this paper that mining of T 3 3 coal beds in Mabukan slope over past hundred of years made upper rockmass tilt outward and subside. It is the direct reason why the rear edge of the slope top is tensiled and collapsed further. If there are no more activities of mining, along with the time going, the slope will be stable by itself. FEM (finite element method) calculation simulated and reproduced the relationship between the development process of tension and subsidence of the rear edge of slope top and mining.