Energy is identified as the most crucial resource of the wireless sensor networks.A significant amount of energy is often consumed by message passing.Many researches have focused on the issues about how to minimize the communication overhead.In-network data processing is a commonly adopted technique,in which an intermediate node called proxy node is chosen to process the source data streams and forward the result to the sink node,thereby reducing the transmission energy consumption.As a result,the optimal selection of the proxy node can minimize the transmission overhead.This paper formulizes the transmission energy consumption of the proxy node selection and proposes an energy efficient selection strategy(EESS),which can greatly reduce the transmission energy consumption of the query without knowing the whole topology of the network.Compared with the method proposed by others,EESS uses fewer control messages and achieves better performance.Simulation results show that EESS performs well even in low-density network and long-distance query,which potentially improves the lifetime of the sensor networks.