Abstract: The concept of lower approximation reduction is introduced in information systems based on dominance relations.And the judgment theorem and discernable matrix are obtained，from which authors can effectively provide the approach to this reduction in inconsistent systems based on dominance relations.Finally，an example illustrates the validity of this method.The proposed framework constructs efficient theoretical basis for knowledge discovery in information systems based on dominance relations.

Key words: rough set, information system, lower approximation reduction, discernable matrix

摘要： 在基于优势关系下的不协调目标信息系统中引入了下近似约简的概念，并得到了下近似约简的判定定理以及辨识矩阵，建立了不协调目标信息系统的下近似约简的具体方法，同时通过实例验证了该方法的有效性，从而为优势关系下信息系统的知识发现提供了理论基础。

关键词: 粗糙集, 信息系统, 下近似约简, 辨识矩阵