This paper addresses the influence of relative density on the particle breakage of non-uniform grading coral sand by 45 one-dimensional compression tests. Dyeing tracking and image segmentation methods are adopted to reveal the particle breakage of the coral sand. The test results show that D-50 (1 mm) is the critical size in deciding the breakage possibility. The number of total broken particles and the broken fine particles (d < 1 mm) increases with the initial relative density. The breakage probabilities of the skeleton particle groups (d < D-50) are significantly greater than those of the fine particle groups (d < D-50). Moreover, the relationship between the relative breakage index and vertical stress for the non-uniform coral sand can be expressed by a power function, which depends on the initial relative density. Furthermore, the most important finding is that the deformation resistance of the non-uniform coral sand is stronger than that of uniform sand. (C) 2021 Elsevier B.V. All rights reserved.