By means of pseudo-dynamic theory, a new calculating method is presented to calculate the pseudo-dynamic seismic active earth pressure behind rigid retaining wall. Considering time and phase difference within the backfills, the horizontal slices is used to analyze the distribution of seismic active force behind retaining wall in more realistic manner. Under the assumption that the soil backfills are rigid body, the equations derived in this paper can be degenerated to Mononobe-Okabe equations. Through numerical analysis, it is shown that the values of seismic active force obtained from present study are smaller than those obtained from Mononobe-Okabe theory and the distribution of seismic force along the depth of the wall is nonlinear. It is also found that the action point of the total seismic active earth pressure is higher than one third of the wall height, which is corresponding to previous experimental results.