In　view　of　the　deficiency　of　the　steel　and　ultra-high　performance　concrete　(UHPC)　composite　bridge　deck　using　the　conventional　mechanical　shear　connectors,　a　type　of　the　assembled　steel　and　UHPC　composite　deck　was　proposed.　To　provide　the　design　and　application　of　the　proposed　composite　deck　with　the　basis,　a　domestic　long　span　flat　steel　box　girder　bridge　was　taken　as　a　reference,　the　steel　deck　of　the　bridge　was　replaced　with　the　proposed　composite　deck　and　the　trial　design　of　the　composite　deck　was　carried　out.　The　ANSYS　was　used　to　create　the　spatial　finite　element　model　for　the　segment　of　the　main　girder　of　the　bridge　and　the　mechanical　performance　of　the　composite　deck　of　the　trial　design　was　studied.　The　results　of　the　study　demonstrate　that　for　the　assembled　steel　and　UHPC　composite　deck,　the　transverse　tensile　stress　of　the　UHPC　layer　and　the　transverse　shear　stress　of　the　binding　layer　are　the　control　indices　of　the　structural　calculation.　In　the　composite　deck,　the　maximum　tensile　stress　subjected　by　the　UHPC　layer　is　10.87　MPa,　the　maximum　shear　stress　subjected　by　the　binding　layer　is　0.97　MPa　and　the　materials　mentioned　herewith　can　all　meet　the　mechanical　requirements　of　the　structure.　The　maximum　stress　range　of　the　worst　structural　detail　of　the　steel　deck　in　the　composite　deck　merely　accounts　for　of　that　of　the　pure　steel　deck,　showing　that　the　structure　of　the　composite　deck　can　accommodate　the　requirements　of　the　practical　bridges　and　can　effectively　avoid　the　deteriorations　like　the　fatigue　cracking　of　the　steel　deck.　©　2018,　Journal　Press,　China　Railway　Bridge　Science　Research　Institute,　Ltd.　All　right　reserved.