We present a cluster-based virtual multiple-input single-output (vMISO) multihop cooperative transmission protocol in wireless sensor networks. In order to construct the cooperative transmission, we arrange each hop into two consecutive time slots: the intra-cluster slot, that accounts for data sharing within the cluster, and the inter-cluster slot for transmission between clusters. In this protocol, we investigate a novel optimal cluster formation method and best cooperative transmission routing selection base on the network energy consumption status. Also, an optimization model is developed to find the optimum number of cooperative nodes, clusters and transmission rates. Simulation results show that the protocol can save energy significantly.