The phenomenon of particle crushing within coral reef sands exerts a significant influence on their mechanical properties. With the aim of investigating the governing laws of particle size evolution throughout the crushing process, a lateral confinement compression test on coral reef sand and gravel was conducted to quantify particle size variations during the assay. The results show that: after hydrostatic compression molding, the percentage of coral reef sand particle size in the range of 19.5–31.5, 9.5–19.5, 4.75–9.5, 2.36–4.75 passes through increased by about 10%. While the particle size distribution within the crushed stone mixture remained largely unchanged, the fragmentation rate of coral reef sand, when assessed under identical grading conditions, is significantly higher than that of crushed stone. The investigation into particle crushing phenomena provides critical insights for guiding related engineering and production methodologies.