Abstract: In transition from open pit to underground mining of Huangmailing Phosphate Mine，such issues as selecting reasonable filling materials，material proportion，and reasonable width of room and pillar should be faced with.For these，the proportion experiments of backfilling were made.Combined with the physical and mechanical parameters of the filling body，the numerical simulation on ore block was carried out by the FLAC3D to verify the actual strength of filling body.By this method，the stability and safety problems of ore block with different parameters were estimated.Studies showed：tailings in Huangmeiling tailing dam has good filling property.The 28d strength of filling body in different proportion varies from 0.18 to 2.48 MPa；The limited width of different filling body to maintain the stability is between 18 and 25 m；The pillar adopted the full-tailings cemented filling with cement-sand ratio of 1∶6，while the room adopts the water and sand back-fill，and both has the reasonable widths at 15 m.

Key words: Cemented filling with tailings, Strength of filling, Stope parameters, Numerical simulation