For smart street light wireless sensor networks, there are huge number of redundant packets flooding in the route discovery process, resulting in information explosion and high energy consumption. This paper proposes an improved flooding routing protocol, during the route discovery process, each node could receive signals such as the serial number of packets copies, destination address, node types and so on, the algorithm will judge whether the received signals need to be continue forwarded in a certain forward probability or not. Thus, the total forward times will be reduced and accordingly the information explosion could be prevented and the energy consumption could be reduced without reducing the reliability. Simulation experiments are conducted on MATLAB, and results show that the improved algorithm has much more higher flooding efficiency than the traditional flooding routing algorithm, and a very broad application prospect to balance the efficiency versus the reliability of the whole networks.