Abstract: Based on stress analysis of the potential sliding mass of tailings dam，and considering the impact of saturated tailings dynamic pore water pressure and filling time on the dam stability，the calculation formula of safety factor for tailings dam in earthquake and post-earthquake had been derived，and the impact of dynamic pore water pressure on the work state of dam was explored.The analysis showed that the dam work state in earthquake is mainly controlled by the reduction of tailings strength and the dam inertial effects; the yield seismic coefficient is significantly affected by the cumulative effect of the dynamic pore water pressure.With the increase of the vibration times，dam yield seismic coefficient is getting smaller and smaller.A critical value of internal friction angle was introduced to distinguish the ultimate failure mode of the tailings dam，called the flow-type damage and the sliding-type destruction.In addition，the failure mechanism and the failure process of the two modes were respectively investigated.

Key words: Tailings dam, Damage mechanism, Earthquake, Critical internal friction angle