Abstract: Particle breakage is an important factor affecting the deformation and strength mechanism of granular soil. In order to study the particle breakage characteristics of calcareous sand during shearing and their influences on the deformation and shear strength, several drained triaxial shear tests are performed on three kinds of calcareous sand with different initial particle-size distributions under varied confining pressures. The results show that the initial fractal particle-size distribution maintains a relatively strict fractal characteristic in the triaxial shear process. This phenomenon can be well explained by the behavior that the broken particles in each particle fraction are mainly added to the adjacent next-level particle fraction. The stress-strain characteristics of calcareous sand are related to confining pressure and distribution of initial particle size. The lower the confining pressure, the more uneven the distribution of initial particle size, the more significant the dilatancy effect of calcareous sand. As the confining pressure increases, the dilatancy tendency of calcareous sand decreases and gradually transits to the shrinkage state. The breakage index of calcareous sand increases with the increase of stress and strain in the shearing process. The peak angle of internal friction decreases with the increase of breakage index, and finally tends toward a fixed value. A non-linear exponential function is used to describe the correlation between the peak angle of internal friction and the breakage index, and it represents the effect of particle crushing on the shear strength of calcareous sand.