The　prestressed　RC-UHPC　composite　box　girder　with　high　tensile　strength　and　corrosion-resistant　ultra-high　performance　concrete　(UHPC)　as　the　web　and　bottom　plate　and　reinforced　concrete　(RC)　as　the　top　plate　was　proposed,　and　a　specimen　was　fabricated.　The　flexural　test　was　carried　out　to　analyse　the　crack　development　pattern　and　damage　mode　of　the　specimen;　the　finite　element　software　was　used　to　simulate　the　test,　and　the　calculation　accuracy　was　verified　by　comparing　the　finite　element　calculation　results　with　the　testing　data,　on　the　basis　of　which　19　finite　element　analysis　models　were　established　to　analyse　the　influence　of　various　parameters　on　the　cracking　moment;　relevant　codes　and　existing　literature　were　used　to　investigate　the　cracking　moment　of　the　prestressed　RC-UHPC　composite　box　girder.　The　results　show　that:　the　first　crack　appeared　when　the　specimen　was　loaded　to　about　33.3%　of　ultimate　load;　the　cracking　moment　was　influenced　by　the　prestressing　bar　tension　factor,　the　prestressing　bar　reinforcement　ratio　and　the　tensile　strength　of　UHPC;　the　cracking　moment　calculation　method　based　on　the　conversion　section　and　the　crack　width　calculation　formulas　in　DBJ　43/T　325—2017　were　used　to　calculate　the　cracking　moment　and　crack　width　of　the　prestressed　RC-UHPC　composite　box　girder,　respectively,　and　the　calculated　values　agreed　well　with　the　testing　and　FE　results.　©　2025　Chongqing　University.　All　rights　reserved.