The event chain of the urban major crisis was established,and the correlation of the various status was analyzed.Based on SEIS epidemic model ,a dynamics model for urban of events,the developing trends and disciplines of the events from normal to crisis was proposed.By analyzing on Situations ,namely with and without the exterior factors affecting on the chain of events,the developing trends and disciplines of the events from normal to crisis were described.Finally,the solutions were analyzed using the Lyapunov stability theory and the simulations.The research showed that the self-repairing capability and the external affecting are the essential factors for the urban crisis.