To　solve　the　typical　damages　such　as　cracking　of　the　pavement　in　the　negative　moment　region　of　steel　bridges　and　steel-concrete　composite　structures,　ultra-high　ductility　cementitious　composites　(UHDCC)　was　developed.　The　experimental　research　on　the　bending　performance　of　steel　-　UHDCC　composite　test　beams　in　the　negative　moment　region　was　carried　out　based　on　theoretical　analysis,　model　experiments,　and　numerical　simulations.　Three　sets　of　single　U-ribbed　steel-concrete　composite　beam　experiments　were　completed　to　investigate　the　bending　capacity,　stiffness,　section　strain　distribution　characteristics,　and　crack　propagation　mode　of　the　test　beams　in　the　negative　bending　moment　zone.　The　formula　for　the　ultimate　flexural　bearing　capacity　of　steel　UHDCC　composite　beams　was　derived　based　on　plastic　design　theory.　And　the　parametric　study　on　ultimate　flexural　bearing　capacity　was　conducted　through　finite　element　model.　Experimental　results　demonstrated　significant　enhancement　in　the　cracking　load,　ultimate　load,　and　bending　stiffness　of　the　Steel　-　UHDCC　composite　test　beams　compared　to　the　Steel　-　NC　composite　test　beams.　Then,　the　steel　-　UHDCC　composite　beams　were　mainly　characterized　by　microcracks,　showing　a　fine　and　dense　distribution　of　cracks.　In　addition,　the　finite　element　parametric　analysis　shown　that　the　thickness　of　UHDCC　pavement　had　the　greatest　impact　on　the　ultimate　bending　capacity　of　composite　beams,　followed　by　the　reinforcement　ratio　of　rebars,　and　the　influence　of　shear　connector　distance　was　relatively　small.　Finally,　the　formula　for　the　ultimate　flexural　bearing　capacity　of　steel　UHDCC　composite　beams　was　derived,　and　the　deviation　rate　met　the　design　accuracy　and　engineering　application　requirements.　The　research　results　of　this　manuscript　can　provide　theoretical　reference　for　the　design　of　steel　-　UHDCC　composite　bridge　deck　structures.　©　2025　The　Authors