For　ductile　materials　with　cracks,　when　the　stress　at　crack　tip　exceeds　the　yield　strength,　a　plastic　zone　will　be　formed　around　crack　tip.　In　this　paper,　the　extended　finite　element　method(XFEM)　in　ABAQUS　was　used　to　simulate　the　crack,　and　the　mechanical　behaviors　of　crack　tip　plastic　zone　under　different　constitutive　models　were　studied　by　taking　the　three-point　bending　specimen　as　the　research　object.　The　COD　experiment　and　theoretical　verification　of　three-point　bending　demonstrate　the　effectiveness　of　this　method.　The　effect　of　the　plastic　modulus　on　size　of　crack　tip　plastic　zone　under　the　double　broken　line　constitutive　model　is　analyzed,　and　the　effects　of　the　load　on　plastic　zone　size　and　stress　distribution　near　crack　tip　under　the　true　stress-strain　constitutive　model　is　discussed.　Finally,　the　difference　of　stress　distributions　around　crack　tip　obtained　from　two　constitutive　models　is　compared.　©　Published　under　licence　by　IOP　Publishing　Ltd.