Abstract: Effect of particle breakage associated with the mechanical behaviour of coral sand has been widely investigated, but not under three-dimensional stress state with different stress paths and loading directions. In this study, a series of true triaxial tests with different test conditions were conducted on two grades of coral sand for this purpose. Before testing, the particle characteristics of coral sand and particle orientation of specimen were investigated, showing that the particles have highly irregular shape, extremely rough surface and abundant pores, and the specimen exhibits significant cross-anisotropy. After testing, the particle size variation of coral sand was also analysed to explore the law of particle breakage with incorporating the effects of intermediate principal stress and cross-anisotropy. Test results show that (1) in the constant minor principal stress tests, as the intermediate principal stress coefficient (b-value) increases, the peak deviatoric stress increases and then decreases under drained conditions, but continuously decreases under undrained conditions; (2) coral sand specimens loaded along different loading directions or stress paths exhibit significantly different strength and deformation characteristics; (3) a unique relationship between relative breakage index and modified input energy is established by introducing a cross-anisotropy correction factor, independent of b-value and other test conditions.