The granularity is used to describe decision knowledge based on the concept of rough degree in rough theory. The rule distance are put forward, and a feasible distance formula between different rules is constructed according to the requirement of describing the distance between different rules and the definition of attribute signification in information system. Both of the n-dimensional knowledge granularity decision space and the same construction mapping decision space based on multi-decision sorts are established, and the decision algorithm is further presented. As a result, the instance is introduced to explain the efficiency of new method.