The settlement of a soft-soil foundation due to earthquake is a considerable threat to buildings. To accurately calculate this settlement, a great number of studies have been carried out regarding the deformation characteristics of soft soil under dynamic loading, and a variety of empirical formulas have been proposed. These formulas, however, are not easy to apply by engineers without specific training because there are a large number of parameters and the experiments are complex. Based on the results from drilling sampling, wave velocity tests, and indoor static and dynamic triaxial tests, we obtained the static and dynamic parameters of 16 soil specimens at nine different depths in the coastal region of Tianjin, which experienced a large settlement following the 1976 Tangshan earthquake. We grouped the specimens into three categories with respect to their components and density, and used relatively simple models and the least squares method to fit the change law of the residual strain and the degradation index of the specimens. The research results show that:(1) The density of soft soil can be used to determine its composition and dynamic characteristics, and also as a main parameter to establish the relationship between the static and dynamic characteristics of soft soil. (2) Silty soil and shell interlayers can increase the modulus of soft soil. To obtain accurate parameters, the soil layers should be classified carefully before performing experiments. (3) The experimental results suggest that exponential models are advantageous when doing regional research on the deformation characteristics of soft soil under dynamic loading. (4) Dynamic loading has little influence on the degradation index of soft soil. In addition to these results, this study also provides some references and basic data for future research on the dynamic characteristics and seismic settlement of soft soil.