As　a　new　type　of　floor　systems,　the　steel-concrete　composite　slim　floor　has　the　advantages　of　low　structural　height,　fast　construction　and　good　fire　resistance.　In　this　paper,　a　method　of　determining　the　effective　width　of　composite　slim　beams　and　design　methods　for　the　stiffness　and　loading　capacity　of　composite　slim　floor　with　deep　deck　under　vertical　load　have　been　proposed,　and　its　rationality　has　been　verified　by　the　experimental　investigations　on　a　full-scale　specimen.　By　using　the　proposed　design　methods,　the　effective　width　of　composite　slim　beams　can　be　determined　conveniently.　Meanwhile,　the　internal　force　analysis　and　deformation　checking　can　be　carried　out　easily.