Abstract: Through similar simulation, the failure process of southern Antaibao open-pit slope under open-underground mining were researched, and based on the failure mode and the settlement behavior of the slope, the boundary parameter of southern Antaibao was optimized. The results show: boundary parameter under open-underground mining, namely vertical height of safe mining between open-off cut and the upper slope, is the nuclear factor for open-pit slope stability, No.9 coal seam was the main seam of the slope stability under the composite mining of No.4 and No.9 coal seams. At last, proposed the reasonable vertical height of safe mining should be no less than 131m, thus providing a base for ensuring the slope stability under open-underground mining.