The　combination　of　the　steel-FRP　composite　bar　(SFCB)　and　engineered　cementitious　composite　(ECC)　holds　favorable　applications　in　terms　of　durable　resilient　structures.　However,　a　clear　understanding　of　the　interfacial　bond　performance　of　this　novel　combination　is　currently　lacking.　Therefore,　the　bond　behavior　and　mechanism　of　the　SFCB-ECC　interface　were　investigated　through　direct　pullout　tests.　A　total　of　48　cube　specimens　were　fabricated,　with　the　test　variables　including　bar　type,　bar　diameter,　embedment　length,　and　matrix　type.　The　experimental　results　indicated　that　the　bond　failure　mode　of　SFCBs　and　FRP　bars　differed　from　that　of　deformed　steel　bars,　attributed　to　the　damage　of　resin-rich　ribs　in　relatively　high-strength　ECC.　The　bond-slip　curves　revealed　both　the　fundamental　differences　and　similarities　among　steel　bars,　SFCBs,　and　FRP　bars.　The　Poisson　effect　and　shear　lag　effect　increased　with　a　decrease　in　bar　stiffness　and　an　increase　in　diameter.　The　combined　impact　of　the　interaction　between　the　bar　stiffness　and　diameter　resulted　in　varying　bond　strengths　for　steel　bars,　SFCBs,　and　GFRP　bars,　despite　their　similar　surface　geometries.　A　theoretical　model　for　the　bond　strength　at　the　SFCB-ECC　interface　was　derived　using　the　thick-walled　cylinder　principle　and　subsequently　validated　with　test　data.　Finally,　a　unified　empirical　model　framework　for　predicting　the　bond　strength　of　various　barmatrix　combinations　was　proposed　based　on　the　theoretical　model.　The　accuracy　of　this　method　was　evaluated　using　a　collected　database.