In order to compensate for limitations of microscopic study on loess triaxial tests，taking the loess in Longxi area as an example，the authors established the loess triaxial test model by using PFC3D software and simulating triaxial shear test under the different confining pressures in 0 kPa，50 kPa and 300 kPa． Compared with laboratory triaxial shear test，the numerical simulation test has a guiding role in loess mechanical strength analysis．