Abstract: The triaxial tests of sand by PFC3D(particle flow code in three dimensions) were simulated.The slip model was used to constitute samples of sand.The slip model provided no normal strength in tension and allowed slip to occur by limiting the shear force.Preliminary study on mechanical properties of soil was done by PFC3D numerical simulation through endowing appropriate micro-properties.Good agreement between the results of numerical simulations and laboratory tests was shown.Macro properties of sand samples with various input parameters of particle elements were presented,and the results were valuable for developing soil constitutive models.The emergence and development of shear bands were simulated numerically by PFC3D under different confining pressures.It was shown that the microscopic parameters of granular materials affected markedly the macroscopic response of the noncohesive frictional material.The meaning of this research lies in the fact that PFC mode could break through the limits of real lab tests and make the microcosmic research of soil possible.In addition,some laws were discovered,and it would be helpful to the study of the application of particle to the geotechnical problems in future.