Abstract: Accidents on expressway will disturb the normal state of traffic flow, even cause the traffic jam. To disperse effectively the traffic jam, a proper model is needed to simulate the traffic flow under crowded condition. In this paper, the characteristics of individual vehicles in the jam were studied, firstly. Then the rules of current cellular automaton model (CA model) were improved and a new CA model for the traffic jam was brought forward. With the new model, it is possible to simulate the process of traffic jams propagation and decay, and the rules of the jams decay can be explored. Lastly, the effects of using different control measures for the jams are investigated.