In order to reflect the variation characteristics of the vertical displacement of foundation under dynamic compaction load, the formula for the peak value of the equivalent contact quasi-static force is derived based on the principle of work and power. The numerical model of dynamic compaction is established by the finite element software ANSYS/LS-DYNA, and the dynamic compaction load is simplified to triangular impact load. The settlement calculation method is verified by an actual project of which the soft soil foundation was filled by dynamic compaction in Nantong. The calculation results show that the ratio of the vertical volume variation to the total volume change of the foundation calculated by the proposed method is close to the measured value, and the settlement calculated by the proportion of volume variation representing the energy distribution coefficient agrees well with the measured value. Therefore, the calculation method of settlement after tamping is applicable to dredger fill soft soil foundation.