Abstract: Through the analysis of existing extension models of rough set，an amended unsymmetrical similarity relation is presented.The extension model effectively overcomes the disadvantage of tolerance relation and non-symmetrical similarity relation.The experiment proves that it is more simple and effective for the incomplete information system，and get more information.

摘要： 通过分析现有粗糙集扩充模型，提出了一种修正非对称相似关系。基于该关系的扩充模型有效地克服了容差关系和非对称相似关系的不足。实例结果表明了其对不完备信息系统处理更简单有效，获取的信息更充分。