In this study, we used the Davidenkov model to conduct a fitting analysis on dynamic test data of deep soft soil in the city of Ningbo and then determined the relevant fitting parameters. The fitting results demonstrate that the Davidenkov model can describe the dynamic characteristics of the Ningbo deep soft soil well. We wrote the computation program for Davidenkov model in APDL language using ANSYS software based on the equivalent nonlinear method and verified its correction by the classic earthquake response program SHAKE. The results show that the program is effective and can address the lack of nonlinear constitutive soil models in existing commercial software. We used the above program to compare relevant codes and analyzed the seismic responses of the Ningbo deep soft soil. The analysis results indicate that the soil displacement obtained by the formula recommended by the code is actually greater than expected, which means that the underground structure that was designed according to code is conservative. The research results from this study provide a reasonable method for calculating soil dynamic characteristics and conducting seismic response analysis of deep soft-soil areas.