Due to the sudden, diversity and harmful of the emergency, China's traffic emergency response are facing a lot of difficult, such as lacking decision-making experience, lack of decision-making information, tight for making decision. A decision support system was established for the city traffic emergency control based on Expert system. And the structure of the system was described in detail, focusing on the establishing ways of knowledge base and inference engine. In the emergency incident, the system can formulate strategies of traffic control quickly and effectively, and will enhance our country's traffic management for emergency greatly.