Abstract: The paper studies communities of practice(CoPs)taking advantage of evolutionary game theory. It formulates knowledge transfer benefit function from knowledge reorganization, knowledge agglomeration, cost of knowledge transfer, organization system, knowledge expectation benefit and so on. Then the study analyzes members' knowledge transfer behavior with evolutionary game theory so as to explore steady and sustainable knowledge flow in CoPs. The results show that knowledge receiving and transmitting ability, knowledge agglomeration effect, incentive mechanism of rewards and punishment, cost of knowledge transfer, knowledge heterogeneity, members' knowledge expectation are the factors effecting knowledge flow. Cops can keep steady and sustainable knowledge flow from these five factors.