Abstract: 9 tailing reservoirs in Sichuan province were serious affected by the 8.0 magnitude Wenchuan earthquake. This paper studies the dynamic properties of fine tailings by using triaxial dynamic testing machine in the lab. Seismic mechanism acting on tailings dam was theoretically analyzed. We also study the liquefying mechanism of saturated granule materials as tailings and main factors of influencing tailings dam stability under seismic action. The numerical simulations point out the key parts of the tailing dam which is prone to instability for seismic liquefaction in the earthquake.