This　paper　presents　finite　element　(FE)　modeling　of　the　debonding　behavior　of　fiber　reinforced　polymer　(FRP)-to-concrete　interfaces　subject　to　mixed-mode　loading,　which　is　realized　through　a　peeling　test　of　FRP　composites　externally　bonded　onto　a　concrete　substrate.　A　cohesive　zone　model　(CZM)　is　implemented　into　the　FE　model　to　represent　the　behavior　of　the　FRP-to-concrete　interface.　Two　element　schemes　(orthotropic　plane　stress　element　and　beam　element)　were　employed　to　simulate　the　behavior　of　FRP　composite　plate　in　the　peeling　test.　The　orthotropic　plane　stress　element　scheme,　bearing　a　clear　physical　background　and　with　an　easy　definition　of　the　material　property　parameters　following　the　composite　mechanics,　is　found　to　be　superior　to　the　beam　element　scheme,　and　thus　is　utilized　to　conduct　parametric　studies.　The　influences　of　the　peeling　angle,　the　interfacial　parameters　(i.e.,　the　configuration　of　the　cohesive　zone　models,　the　interfacial　damage　initiation　law　(DIL),　the　interfacial　damage　evolution　law　(DEL),　the　coupling　of　mode-I　and　mode-II　components),　on　the　mixed-mode　failure　of　the　FRP-concrete-interface　are　carefully　investigated.　The　results　showed　that　the　mode　I　component　plays　a　critical　role　in　the　debonding　failure　of　FRP-to-concrete　interfaces　even　when　the　peeling　angle　is　very　small.　The　failure　of　FRP-to-concrete　interface　transits　promptly　from　a　mode　II-dominated　one　to　a　mode　I-dominated　one　when　the　peeling　angle　increases　to　a　relatively　small　value　(e.g.,　4　degree)　and　subsequently　the　peeling　force　(i.e.,　the　debonding　strength　of　FRP)　decreases　dramatically.　Such　mixity　of　the　mode　I　and　mode　II　components　should　be　appropriately　considered　for　refining　the　analysis　of　FRP-strengthened　RC　beams　and　the　FRP　debonding　strength　design,　for　which　a　pure　mode　II　interfacial　failure　was　usually　assumed.