The elasto-plastic finite element method coupled with infinite elements was used to analyze and predict the stability of No.91 orebody in the process of mining,and the numerical method was used to obtain the exposure height of filIbody. In the process of modelling,the step-by-step excavating and the filling effect were taken into account,and the internal loading model that the stress released along the surrounding of excavation was used. As for the location where the fillbody touched with rock mass,the thicknessless joint elements were used so that the filling effect were modeIled effectively.