Unmanned aerial vehicles (UAVs) swarm technology has been a hot topic. The concept of swarm comes from nature, such as the cooperation of bee colony or ant colony, so the research of swarm intelligence (SI) optimization algorithm inspired by swarm activities in nature is beneficial to the development of swarm UAVs technology. The characteristics and principles of eleven SI algorithms are described and analyzed in the paper. The article also analyzed how to combine SI and multi-UAV task assignments. Furthermore, the prospects for development of the SI are discussed.