Abstract: S&T intermediary is an important carrier to optimize the configuration of innovation resources of the cluster , but its specific form of effect is transformed dynamically along with the change of the surrounding environment of the cluster. By collecting the data of 41 transformation and upgrading demonstration area in Zhejiang Province, adopting QCA method to analyze the function of the role of S&T Intermediary in different network structures, it is found that the mechanism of the influence of S&T Intermediary on cluster development can be divided into three types, including co-equal network knowledge dissemination model, intensive network knowledge dissemination model and fragmented network bridge model , the bridge plays a fundamental leading role in all modes. In addition, limited by the total amount of resources and the level of industrial development, diversification of business development of S&T intermediary relying on the innovation chain cannot yet play a significant role in promoting the development of cluster. The result of research provides an effective reference for the rational design of the development path of S&T Intermediary and the optimization of the configuration of scientific and technological resources in cluster.