High-strength　materials　and　corresponding　composite　members　are　gradually　accepted　in　the　bridge　industry　to　achieve　the　purposes　of　large　span　and　lightweight.　Three　simply　supported　I-shaped　steel-concrete　composite　beams　were　tested　to　investigate　their　flexural　behavior　when　different　combinations　of　materials　were　used,　i.e.,　high-strength　steel-ultra　high　performance　concrete　(HS-UHPC),　high-strength　steel-conventional　strength　concrete　(HS-CC),　and　conventional　strength　steel-ultra　high　performance　concrete　(CS-UHPC).　The　test　finds　that　the　HS-UHPC　composite　beam　has　the　highest　flexural　strength　and　reasonable　plastic　deformation　ability　as　compared　to　the　other　two　beams.　A　finite　element　(FE)　model　was　also　constructed　and　benchmarked.　Subsequently,　the　model　was　utilized　to　conduct　parametric　studies,　aimed　at　exploring　in-depth　the　flexural　behavior　of　steel-concrete　composite　beams.　The　results　from　the　tests　and　FE　analyses　were　employed　to　assess　the　suitability　of　existing　design　specifications　(i.e.,　AISC　360-22,　GB　50017-2017,　and　Eurocode　4)　in　estimating　the　flexural　strength　of　HS-UHPC　composite　beams.　The　evaluations　indicated　that　GB　50017-2017　can　reasonably　estimate　the　flexural　strength　of　HS-UHPC　composite　beams.　This　research　provides　valuable　insights　into　the　design　and　construction　of　HS-UHPC　composite　beams　in　bridges.　©　The　Author(s)　2025.