Abstract: According to the engineering practice pf the transition from open-pit to underground in Xingshan iron ore, based on the K.B.LuPei brezhnev's estimation method, the reasonable thickness of boundary pillar in Xingshan iron ranges at between 12.34 to 17.11 m.4 numerical simulation schemes whose boundary pillar thickness are 12 m, 14 m, 16 m, 18 m are built and calculated by using numerical simulation software MIDAS/GTS, and are analyzed from boundary pillar subside, stope pucking, the maximum tensile stress of boundary pillar and the maximum compressive stress of surrounding rock in the stope.It concluded that the optimal thickness of boundary pillar is 16 m.

Key words: Transition from open-pit to underground, Boundary pillar, Safety thickness, Numerical simulation