The seismic acceleration dynamic distribution coefficient suggested in the current code for seismic design of hydraulic structure(DL5073-1997) is suitable for earth-rock dams that are below a height of 150 m. However, currently, most earth-rock dams being designed are higher than 150 m. Compared with low-height dams, tall dams have less constraint from the stiffness of their foundation and the self-vibrating period of the high dam is prolonged under cyclic loading. During the seismic response of the dam body, the high order self-vibrating period has more opportunities to coincide with the seismic predominant period and high order vibrations are easily activated and amplified, which causes the seismic acceleration distribution to be dissimilar to that in short dams. Using the finite element method, the seismic acceleration distribution of high earth-rock dams can be analyzed. The analytical results allow for the determination of the seismic acceleration dynamic distribution coefficient of earth-rock dams 250 m level in height. On the basis of these results, employing a modified Drucker-Prager model and strength reduction technique, further research on the slope seismic stability analysis of earth-rock dams 250 m level in height was made. The conclusion of this analysis was that a decrease of the seismic acceleration dynamic distribution coefficient in the dam body causes an increase in the critical value of safety factor of the dam slope.