Abstract: It was said that the seismic settlement relates to the earthquake intensity, the endurance period, the soil behavior, the structure intensity, the location and the aseismatic means etc.For the technical application, in order to prevent or reduce the damage of the seismic settlement, besides reinforcing aseismatic facilities, it brings definite social advantage and economic benefit to estimate the magnitude of the seismic settlement via numerical calculation in engineering construction.By the effective stress dynamic response analysis with equivalent linearity, this text utilizes the equivalent nodal force method to analyze the variation tendency of the soft clay seismic settlement of a certain highway foundation along with the seismic peak acceleration, and establishes a formula of the seismic settlement which is related with the embankment height, the soft soil dynamic modular coefficient, the saturated unit weight, the ratio of the amplification factor of the vertical seismic acceleration to the horizontal one and the horizontal seismic coefficient etc.Furthermore, the effect of the frequency spectum on the seismic settlement is still be realized taking on some instructiveness for the correlative research.