Abstract: A density-dependent soil constitutive model for large stress range is proposed for the analysis of large deformation of soil subjected to high stresses under dynamic compaction. A rigid-flexible contact algorithm is further developed and the material point method combined with the proposed constitutive model is used to simulate the dynamic compaction process. In contrast to some previous numerical simulations, in which the input load is assumed to be a triangular stress wave, the loading procedure here is achieved by controlling the collision speed between the hammer and the soil. The computed results are in good agreement with the experimental data on the construction site of Chengde Airport. A new concept, the “energy conversion rate” in the process of dynamic compaction, is introduced, and the laws of energy conversion are studied, which provides a new perspective on the study of dynamic compaction. The numerical simulations indicate that an increase in the energy conversion rate does not necessarily mean an increase of the crater depth per impact, since the distribution of energy in a larger domain may result in a lower crater depth under a high energy conversion rate. A greater shear plastic strain energy absorbtion may contribute to a local concentration of the absorbed plastic strain energy in volume compression of soil. It is also found that the energy conversion rate under low drop of a heavy hammer is higher than that under high drop of a light hammer, and consequently produces in general a larger crater depth.