The grain breakage and shear strength of shell sand are studied systematically.Based on the innovation of former grain size distribution curve,a new curve of relative grain size distribution curve is put forward,which reflects directly the change of the grain content in one grain size in the process of grain’s breakage and shows the degree of particle’s breaking briefly.Moreover,the triaxial compression consolidated undrained (CU) tests and drained (CD)tests are analyzed systemically.It points out that the cohesion has more effect on the grain’s breakage than the internal friction angle in the process of grain’s breakage,whereas the internal friction angle takes the initiative to peak stress in the process of strain-stress.When the relative density and confining pressure phase are equal during the test,the peak stress of CD is higher than CU.