Abstract: By using the dynamic finite element stability and deformation method, the definite methods for the most dangerous sliding surface, the influences of seismic duration and depth of sliding surface on slope stability and deformation as well as the reinforcement range of dam slopes are studied. The results show that by means of the pseudo-static method, the slip circle corresponding to the minimum safety factor is deeper and the slip range is larger owing to the fact that the acceleration distribution coefficient suggested by the Chinese Code does not match the seismic response of dams. It is not helpful for determining the reinforcement range of dam slopes. During the earthquake history, the potential sliding surface varies with the time history, and it should be arbitrarily searched by using the dynamic finite element method. The potential sliding surface corresponding to the minimum safety factor is different from the maximum slippage. The estimation of the stability safety of dam slopes should combine the safety factor with the deformation. The reinforcement range of dam slopes is suggested according to the calculated results.