Based on the upper-bound theory of limit analysis, the pseudo-static method was carried out to assess the amplification effects of seismic acceleration on stability of homogeneous earth slopes. The least upper-bound solutions of seismic slope stability are determined and then compared with other results for verification of the presented method. A parametric sensitivity analysis is conducted for the horizontal seismic acceleration at the bottom of the slope and the seismic amplification coefficient to investigate their influences on slope stability. The results demonstrate that the stability of seismic slopes decreases with the increase of seismic amplification coefficient, while the most critical slip surface becomes deeper. Finally, according to the correlation between the factor of safety for seismic slope and dimensionless parameters, a fitting formula is established to calculate the factor of safety for slopes subjected to the seismic amplification. It is convenient for practical engineering to quickly evaluate the influence of seismic amplification effect on slope stability.