Abstract: Some objects in set-valued information systems may have more than one value for an attribute，so a new variable precision tolerance relation is defined by similarity grade of attribute’s et-valued and use maximal consistent block to pose maximal variable precision tolerance classes in set-valued information system，based on it the problem of decision rule’s acquisition，relative knowledge reduction and decision rule’s optimization in set-valued information system are discussed.

摘要： 集值信息系统中对象的属性集值一般不唯一，基于对象属性集值的相似程度在集值信息系统上定义了一种变精度容许关系，并借用极大一致块方法给出了集值信息系统上极大变精度相容类的定义与一些性质，讨论了在这种极大变精度相容类下集值信息系统的决策规则的获取、属性的相对约简及决策规则的优化。