This　paper　proposes　a　new　large　span　half　steel-plate-reinforced　concrete　(H-　SC)　hollow　roof　structure　for　nuclear　power　plants.　The　roof　composes　of　23　I-shaped　H-SC　beams.　Each　H-SC　beam　consists　of　a　steel　plate　assembly　(a　bottom　plate,　a　web　plate　and　a　short　top　plate),　which　is　cast　inside　an　I-shaped　reinforced　concrete　beam.　This　novel　system　not　only　has　an　equivalently　high　bearing　capacity,　stiffness　and　lower　gravity　load　comparing　with　conventional　RC　roof,　but　also　can　be　conveniently　constructed　by　using　the　bottom　plates　as　formworks.　The　numerical　simulation　was　conducted　to　demonstrate　its　mechanical　capacities　and　the　influence　of　construction　process.　Firstly,　a　finite　element　(FE)　model　for　the　H-SC　composes　was　built　and　a　one-third　scaled　12　meters　large-span　H-SC　beam　was　tested　to　validate　the　proposed　FE　model　and　analyze　the　steel-concrete-interface　bond-slip.　Then,　the　numerical　simulation　was　conducted　to　assess　the　effect　of　the　construction　process　on　the　mechanical　performance　of　the　entire　roof　structure,　in　which　the　deactivation　element　and　trace　element　techniques　were　used　to　simulate　the　deformation　induced　by　the　construction　process.　The　results　show　that　the　deflection　induced　by　the　construction　process　accounts　for　87%　of　the　final　deflection.　Copyright　(C)　2019　by　The　Hong　Kong　Institute　of　Steel　Construction.　All　rights　reserved.