基于对某地下水封洞库库区详细的地质调查和研究，运用块体理论评价围岩块体稳定性。采用块体理论分析方法之一的矢量分析法，分析出地下洞库各开挖面的可动块体，通过力学分析判别出可动块体中的关键块体，计算出其剩余下滑力和失稳形式。结果表明：此地下水封洞库稳定性较好，关键块体主要以结构面②,④单面滑动，且主要分布于洞室顶部。因此施工时应重点监测结构面②,④出露处，同时通过分析研究发现矢量法作为块体理论一种分析方法，能准确分析围岩块体稳定性，对地下水封洞库围岩稳定性评价具有一定的意义，但其在确定关键块体的具体位置，以及对于曲面洞壁块体稳定性分析均有待于进一步完善研究。

Based on detailed geological survey and research of a underground watertight cavern, the stability of surrounding rock mass was evaluated by using the block theory. Vector analysis was used to analyze the movable blocks of each cut surface in the underground cavern, and mechanical analysis was employed to find out the key blocks of the movable blocks and to calculate their driving forces and failure modes. We conclude that this underground watertight cavern is stable, with the key blocks mainly sliding by single structural surface ② and ④, and mostly distributed on the roof of the cavern. Therefore, monitoring during the construction should be focused on places where the structural surface ② and ④ were exposed. At the same time, it’s found that the vector method could accurately evaluate the stability of surrounding rock blocks, but is needed to be improved when determining the specific location of key blocks and analyzing the stability of curved cavern walls.