Abstract: Laboratory triaxial shear tests on shell sand taken from Meizhou Bay of Putian, Fujian are presented under different confining pressures, relative densities and sample sizes. A grading entropy model is proposed to measure the particle breakage degree after triaxial compression based on the statistical entropy concept with dataset of particle size distributions. This methodology is also compared with Hardin particle breakage model. It is shown that the quantity of particle breakage of shell sand is affected by the confining pressure, relative density and the sample size. With the increase of the confining pressure and sample size, the quantity of particle breakage of shell sand increases under the same experimental conditions. When the relative density is low, the quantity of particle breakage tends to increase. While the relative density reaches a higher value, the particle breakage is weakened. The particle size distributions of shell sand before and after triaxial compression can be characterized by the grading entropy parameters, in which the relative base entropy parameter (NB) reflects the degree of particle breakage. The higher degree of particle breakage, the lower value of NB. There is a significant linear relationship between NB and Hardin's index. The behavior of particle crushing of shell sand can be greatly described by the grading entropy parameters, which may be a useful index for the quantitative analysis of the particle breakage of geotechnical materials.