Abstract: The architecture and mechanism of coalition formation that cooperate in multi-agent systems,based on set partitioning,rough sets,large systems cybernetics and artificial society theory are studied.Two kinds of coalition architecture and six kinds of coalition model are presented.Several concepts,such as the concept of degree of coalition accuracy,are presented from the point of view of the knowledge capability.The algorithm of coalition formation is described and analyzed.The algorithm is easy to implement.An application example is given.These work presented an effective approach to solve the vague boundary region problem of knowledge sets made up of the capability and task of agent.