Abstract: To solve the problem that it is difficult to obtain the characteristics of particles motion trajectory and local void ratio change in the critical state of soil in laboratory tests.Several conventional triaxial numerical models of granular materials with different initial states under flexible boundary conditions was established by DEM to contrast the evaluation characteristics of shear bands and the differences in the overall void ratios and local void ratios of granular materials with different initial void ratios.The numerical results show that:The sand specimens with a larger initial void ratio are more likely to form shear bands in the loading process.The particles in the shear region rotate violently with the loading,and the flow of local particles is turbulent.The particles out of the shear zone rotation are not obvious,and the flow shows directional characteristics.For sand samples with different initial void ratios,the critical state void ratios on the shear band and the deviator stress ratio are independent of the initial void ratio,and the stable characteristics of the constitutive tensor invariants of the critical state characteristics indicate that the critical state exists and is unique.