In order to have a safety mining in the steep inclined seam under a water body, based on the geological condition of the hydrological project in the steep inclined seam of the South No. 2 Mining Block in Longhu Mine, a discrete element UDEC2D humerical calculation was applied to analyze the factors affected to the stability of the water prevention coal pillars for the mining operation in the steep inclined seam. The results showed that with the mining thickness of the steep inclined seam increased and the coal strength decreased, the falling down scope of the water prevention coal pillar would be increased in tendency. The key stratum existed in the overburden strata and the broken and rotary of the rock beam in the immediate roof both caused the falling down scope increased of the water prevention coal pillar. When the elastic modulus of the backfill mass reached at 0. 5 GPa, the falling down and failure scope of the water prevention coal pil- lax would be reduced by 54. 3%. Therefore, according to the data calculation results of the site, a roof control technology with coal rejects self sliding backfill and grouting bound backfill mass was determined for the mining goal in the steep inclined seam. Meanwhile the reinforcement measures of the water prevention coal pillar would effectively ensure the stability of the water prevention coal pillar during the mining period of the steep inclined seam.%为实现水体下急倾斜煤层的安全回采，基于龙湖煤矿南二采区急倾斜煤层的水文工程地质条件，采用离散元UDEC^2D数值计算，分析了急倾斜煤层开采防水煤柱稳定性的影响因素。结果表明：随着急倾斜煤层采高的增大和煤体强度的降低，防水煤柱的垮落范围呈增大趋势；覆岩中关键层的存在以及直接顶岩梁的破断旋转均导致防水煤柱的垮落范围增大；当充填体弹性模量达到0．5GPa时，防水煤柱的垮落破坏范围可以降低54．3％，根据数值计算结果确定了急倾斜煤层采空区矸石自溜充填并注浆胶结充填体的顶板控制技术，同时采取了防水煤柱加固措施，有效确保了急倾斜煤层回采期间防水煤柱的稳定。
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