Abstract: The increasing of expressway traffic quantity has brought forward a higher request on expressway traffic control. The traditional traffic control methods based on precise mathematics models is complex and the effects of their application always can not reach the expectation, so developing a new control method is necessary. Multi-agent technology is a hotspot in the artificial intelligence field. One agent controls its object autonomically and initiatively. Between two agents there is a cooperation which can improve the intelligence of the whole system. This paper introduced the concept of the Multi-Agent System(MAS), and described the architecture of the expressway traffic control system based on multi-agent and the functions of modules inside agent. A brief analysis of the cooperation between agents was presented. The expressway traffic control system based on multi-agent technology, which is an intelligent traffic control system with new architecture, can overcome drawbacks of the traditional traffic control methods and can adapt well to the complexity and randomicity of expressway traffic. The key of MAS technology is the cooperation between agents. Consequently the next research should be focused on how to build an effective mechanism of cooperation between agents.