During earthquake disasters, the consolidation seismic subsidence of soft clayey soil in the coastal areas could cause the damages of building subsidence, collapse, and non-uniform settlement. Therefore the research on the consolidation seismic subsidence of soft clayey soil and the method for estimating seismic subsidence are the important subject. Based on the equivalent stress principle of soil dynamics, the problem of consolidation seismic subsidence on loading and unloading conditions is simplified to the general consolidation problem, and the variations of extra-static pore water pressure of soft clay in one-side and two-sides drainages are discussed. Furthermore, a relative simple method for seismic subsidence estimation is put forward and it is validated by the data collected from Wanghailou residential area of Tanggu, Tianjin. The result indicates that the seismic subsidence is 46.1 cm with two-side drainage while 25.7 cm with one-side drainage. Based on field data of the area, the seismic subsidence of silty loam area is 30 cm-40 cm with 15 cm-20 cm in silty clay region, and the largest subsidence is 60 cm. Therefore, the modeling result is consistent with field data.