Dynamic compaction method is widely used for its high efficiency in foundation treatment. But the vibration caused by dynamic compaction will threaten the surroundings especially the structures around. Base on the fact that the tamping energy is approximately divided into vibrational energy and plastic work of soil, the formula of plastic work is derived according to the proposed ellipsoid partition model of dynamic compaction, and the inversion method of the energy efficiency is given by monitoring the information such as depth of tamping pits；also the inversion formula is derived. According to the ellipsoid distribution hypothesis of the affected zone and compacted zone, associated with the monitoring data of the depth of tamping pits, the calculation method of compacted scope and affected scope is given. Finally, under the background of the Beijing Garden Expo Park backfill soil reinforcement project, the compacted scope and affected scope as well as energy efficiency of dynamic compaction are calculated and inversed according to the field monitoring information. The result shows that the method in this paper can not only inverse the energy efficiency and calculate the compacted scope and affected scope, but also provide a reference to estimate the effective number of tamping in the design of reinforcement scheme. By comparing the analytical results with the foundation testing results, the effectiveness and practicability of the method in this paper are verified.