To　study　the　properties　of　the　interfacial　transition　zone　(ITZ)　of　recycled　aggregate　concrete　(RAC),　a　RAC　model　was　presented　that　can　mesh　directly　inside　the　aggregate.　The　characteristics　of　the　ITZ　can　be　accurately　identified　and　simulated　based　on　this　model.　Additionally,　as　for　comparative　specimens,　several　projection　mesh　models　of　RAC　were　also　set　up　to　prove　the　accuracy　and　efficiency　of　this　model.　Further,　a　two-dimensional　(2D)　element　was　introduced　to　simulate　the　ITZ　element,　which　is　degenerated　from　a　three-dimensional　(3D)　element　on　the　base　force　element　method　(BFEM).　Hereafter,　these　RAC　models　were　subjected　to　a　displacement　loading　to　simulate　the　uniaxial　compression　and　tension　tests　based　on　the　BFEM.　The　effect　of　ITZ　thickness　on　the　compressive　strength,　tensile　strength,　peak/ultimate　strain,　and　crack　development　was　studied.　Besides,　the　influence　of　the　relative　properties　between　ITZs　and　the　corresponding　mortar　was　also　investigated.　The　obtained　results　demonstrate　that　the　present　model　is　an　efficient　way　to　analyze　the　influence　law　of　ITZ.　Besides,　the　multiple　influencing　factors　can　be　fixed　via　this　model;　therefore,　their　effects　can　be　studied　by　varying　one　single　factor　at　a　time.　The　degenerate　element　is　a　new　approach　to　investigate　the　element　with　a　large　aspect　ratio　with　sufficient　accuracy　and　efficiency.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.