Both energy efficiency and robustuess are critical design challenges to large scales wireless sensor networks.Applications such as query propagation rely regularly on network-wide flooding as a robust way while frequent flooding consumes too much energy and bandwidth.The effect of packet size on the energy efficiency,and the impact of the transmission radius on the average settling time in which all nodes finish transmitting the flooded packet are analyzed in this paper.A bi-level programming model is imported:the upper level model aims to minimize the average settling time of flooding and the lower level model maximizes the energy efficiency of the whole network.Furthermore,one numerical example is introduced to validate the programming model which shows that the result is feasible and efficient.