Abstract: Gravelly soil is widely used as backfill materials in sea reclamation and valley filling. Dynamic compaction is a priority method to treat gravelly soil foundation. It is important to study the fracture mechanism of gravelly soil under dynamic compaction. In the research, the relative particle breakage rate is chosen as the quantification index of particle breakage. The particle breakage test reveals the positive correlation between relative particle breakage rate and confining pressure, and determines the reasonable fitting formula. It indicates that the more pressure caused by dynamic compaction, the deeper the particle breakage. It is found that the peak internal friction angle of gravelly soil decreases with the increase of particle breakage. The weakening of this strength parameter should be paid more attention to in the treatment of gravelly soil. The dry density and pore ratio of the samples increased and decreased linearly with the increase of the relative particle breakage rate, which reflected the compacting process of gravelly soil under the action of dynamic compaction. The particle breakage can improve the gradation of gravel soil, making it easier to reach the dense state, which is an important meso-scopic mechanism of treatment by dynamic compaction of gravelly soil.