Abstract: The crushing of particles is one of the important factors that cause change of the sand mechanical properties, in particular the fragile material calcareous sand. This paper aims to further understand the effect of particle crushing on the stress-strain and shear strength of calcareous sand. It carries out a series of triaxial shear tests on calcareous sand with different relative densities under different confining pressures. It analyzes the particle size distribution curves of calcareous sand samples before and after tests. It discusses the particle breakage rules of calcareous sand as well as their influencing factors. Through triaxial tests the stress-strain curve of the calcareous sand is obtained. The relationship between relative density and particle crushing, confining pressure and particle crushing, and the effect of particle crushing on stress-strain and shear strength of calcareous sand were analyzed by introducing Hardin's relative breaking ratio Br. The results show that with the increase of confining pressure, the increment of particle shrinkage decreases gradually until the crushing reaches an upper limit. Then the confining pressure and relative density have little effect on the particle crushing. The influence degree of relative density on particle crushing is less than confining pressure. Sliding friction can bring about the stress increase to a limit state. The particle crushing result in the stress cannot reach the state. In the experimental condition, particles are less broken under low confining pressure and the relative motion form among particles is slip, so the stress-strain curve is soften strain type. Under high confining pressure the particles crushing becomes serious and occurs throughout the shear process. So the stress-strain curve is hardening strain type. Particle breakage makes the volume gradually change from the dilatancy to the shrinkage. The more serious the breakage is, the more obvious the shrinkage is. Under low confining pressure the strength of calcareous sand is mainly provided by dilatancy and interlocking. Due to the serious particles breakage under high confining pressure, the dilatancy disappears and the interlocking decreases, so the peak friction angle decreases and the shear strength reduces.