Abstract: By adopting the idealized granular materials (DEM sphere), artificial materials (glass bead) and natural materials (Hostun sand), the grading effect on the stress-strain and the critical state behavior of granular materials is investigated through numerical and conventional drained triaxial tests. The results reveal that for the samples with the same initial loading conditions (e₀ = 0.574, p'₀ = 400 kPa), granular materials with a wider particle distribution display more contractive behavior and also strain hardening upon shearing. Furthermore it is found that the critical state line in the e-p' plane shifts downward as grading broadens with an increase of the coefficient of uniformity C_u, whereas the critical state line in the q-p' plane appears to be independent of the coefficient of uniformity C_u.