To formulate a reasonable and effective urban seismic traffic evacuation plan, this paper applied modified equivalent length, analysis of the factors which influence the seismic evacuation process, using the improved equivalent length to instead of the actual road network, this paper put forward an improved seismic evacuation dynamic traffic assignment model which is based on CTM. Experimental results show that the model can either be multiple origin-destination network optimization problem simplified into single origin-destination traffic assignment network optimization problem, and can be properly reflected the dynamic characteristics of the evacuation traffic flow, and can be satisfied the dynamic allocation demand of traffic evacuation simultaneously.