Wireless sensor networks have developed with recent advancement in wireless communication and electronics. However, a system of sensor nodes is highly energy constrained. Limited energy resource to the sensor becomes an obstacle for its applications. Recently, data aggregation or fusion techniques for energy saving in wireless sensor networks have been the focus of research efforts, but they are insufficient to support advanced fusion applications. We extend these techniques to future sensor networks and proposed an architectural of fusion model build on network layer. Furthermore, this paper discusses the connection between the fusion level and energy consuming. Then various fusion techniques for minimizing the transmission cost in network are introduced. At last, a practical case shows that fusion approach for saving energy in wireless senor network is very efficient.