With distributed power access, Network reconfiguration and other technology, Traditional power system fault diagnosis and fault location of large-scale grid has some limitations. This paper proposes a fault location method for Smart grid base on MAS of Rough Set theory. To solve the issues that the fault diagnosis decision-making needs load computational capacity and flexible network structure mutations. The method uses the group decision-making feature of Agent; divides the network area into the associated regions by the matrix for described the network area, then using rough set theory to a small area fault location in the node sets. The method combines the characteristics of a distributed network that the parallel processing of MAS and easy to expand and modify. Fault location by it has better flexibility and faster reaction speed.