Numerical　simulation　of　triaxial　test　are　carried　out　for　soil　specimens　with　varying　particle　size　by　DEM　analysis　under　the　flexible　boundary.　For　the　purpose,　soil　state　characteristics　such　as　shear　band　formation,　variation　law　and　the　difference　between　the　global　void　ratio　and　the　local　void　ratio　are　particularly　focused.　Results　shows　that　the　shear　band　of　multi-graded　specimen　is　more　difficult　to　create,　but　it　is　thicker　than　that　of　single-graded　specimen.　Overall　void　ratio　changes　mostly　due　to　particle　movement　at　the　shear　band　and　independent　to　particle　gradation.　The　shear　strength　of　the　multi-graded　sample　is　better　than　that　of　the　single-graded　specimen.　Copyright　©　2022　Chenglong　Jiang,　et　al.　This　is　an　open　access　article　distributed　under　the　Creative　Commons　Attribution　License,　which　permits　unrestricted　use,　distribution,　and　reproduction　in　any　medium,　provided　the　original　work　is　properly　cited.