Abstract: In Jinchuan No. 2 Mine Area, the backfilled mining in large hypogeal area without jambs have resulted in the two mining levels at two different altitudes, respectively above and under the altitude of 1150 m, and the ore-body between them is called a horizontal jamb. Each of the two mining levels is distinguished seven mechanized panels along the lode from east to west. Under the altitude of 1150 m, between the third and the forth panel on the down mining level, a vertical jamb 20~30 m in width in the lode direction isn’t mined for preventing the horizontal jamb from submergence. The vertical jamb in 2004 has already reached 50 m in height, the mine engineers wondered whether or not the vertical jamb would be allowed to become higher without mining in the future. A three-dimensional finite element mechanical model is established to simulate the yield failure process of the horizontal and vertical jambs within the changed tectonic stress field caused by continuous mining. The results indicate that the yield failure process begins at the centre, and then spreads to the top and the bottom within the vertical jamb, and in 2005, almost all part within the vertical jamb attains the failure situation. Based on the simulated results, it is considered that the support effects of the vertical jamb on the horizontal jamb and on the hanging wall and footwall rocks will gradually weaken because of the failure of the vertical jamb. Because the failure of the vertical jamb cannot evidently affect the distribution of the tectonic stress field in the mine area, it is suggested that the vertical jamb should be canceled on the down mining level in the future deeper exploitation besides the upper existent part.