<p>The influence of expanded polystyrene (EPS) particle volume ratio on the dynamic deformation characteristics of lightweight soil was explored using laboratory dynamic triaxial tests and distinct element numerical simulation. Macro-hysteresis curves and the distributions of micro-contact force, velocity field, and displacement field were obtained. The results revealed that the attenuation amplitude of the dynamic strength increased with an increase in the EPS particle volume ratio. Unloading simply reduced the displacement of the particles, while the displacement direction still pointed from the two ends of the sample toward the middle, which resulted in macroscopic compression deformation of the sample. With an increase in the EPS particle volume ratio, the sample was more prone to damage. This observation is consistent with the decrease in dynamic strength of the sample with macroscopic increase in the EPS particle volume ratio.</p>