Knowledge building is a meaning making process with social negotiation and dialog. In the new environment adapting to the group learning context supported by synergistic learning toolkits, this study explores the community structure , social relation and participation character in classroom knowledge building by Social network analysis. This results show that there come into being a social relation network with knowledge convergence under the learner knowledge building led by teachers, which make views and ideas of learners assembling to support knowledge building, at the same time this paper also describes the participant character in learning community. This study can provide a new way to learning technology innovation in different culture context.