The　discrete　element　method　(DEM)　can　elucidate　the　macroscopic　property　changes　caused　by　the　breakage　of　granular　materials　from　a　microscopic　perspective.　In　this　paper,　the　fragment　replacement　method　(FRM)　volume　expansion　method　is　used　to　establish　the　DEM　model　for　triaxial　tests.　Through　numerical　simulations　of　breakage　and　non-breakage　of　specimens　with　different　gradation　groups　of　characteristic　particle　sizes,　the　influencing　factors　of　breakage　and　their　microscopic　responses　are　determined,　and　the　critical　states　of　crushed　specimens　are　investigated.　The　results　show　that　the　shearing　dilatancy　characteristics　of　each　specimen　are　governed　by　the　stress　level,　and　the　dilatancy　decreases　as　the　stress　increases;　the　differences　in　the　macroscopic　mechanical　properties　of　the　specimens　of　different　gradation　groups　originate　from　particle　fragmentation　degree　and　the　different　particle　contact　effects;　the　characteristic　state　stresses　of　the　specimens　with　different　characteristic　particle　sizes　are　linear　in　the　p-q　plane,　where　q　is　the　critical　shear　stress　and　p　is　the　mean　principal　stress;　as　the　content　of　fine　particles　decreases,　the　amount　of　breakage　increases,　and　the　line　of　the　critical　state　void　ratio　shifts　down　and　deflects　more;　at　low　confining　pressure,　particle　breakage　mainly　occurs　at　the　early　stage　of　shear,　while　at　high　confining　pressure,　particle　breakage　accompanies　the　whole　shear　process.