Based　on　the　theoretical　analysis,　the　FEM　simulation　and　a　series　of　model　tests,　the　cracking　behaviors　of　FRP-concrete　interface　are　analyzed.　The　results　show　that:　the　interfacial　cracking　of　FRP　strengthened　RC　beams　can　be　analytically　calculated　with　the　fracture　mechanics　method,　and　the　theoretical　solutions　accorded　well　with　the　FEM　results.　The　interfacial　stress　intensity　factor　of　mode　I　is　sensitive　to　the　FRP　debonding　angle.　When　the　FRP　debonding　angle　is　large　the　interfacial　cracking　is　I　and　II　mixed-mode　fracture,　but　considering　that　the　alternate　dimensions　of　shear　cracks　are　quite　little　according　with　the　member　length,　the　interface　of　FRP　strengthened　RC　beams　mainly　exhibits　as　mode　II　cracking.　The　interfacial　mode　II　stress　intensity　factor　is　proportional　to　the　square　root　of　concrete　strength　or　that　of　FRP　stiffness,　and　increases　linearly　with　the　increase　of　FRP　strain.　In　the　model　tests　three　evolution　processes　of　the　stress　intensity　factors　along　with　loading　are　observed,　in　which　the　dividing　points　are　the　concrete　cracking　and　the　steel　reinforcement　yielding.　The　interfacial　critical　stress　intensity　factor　is　about　5.91MPa　·m0.5　At　last　the　FRP　debonding　strain　is　given　according　to　the　tests,　and　the　interfacial　debonding　can　be　effectively　avoided　by　limiting　the　FRP　strain　in　the　range　of　the　debonding　strain.