The invention discloses a prefabricated floor slab reinforcement cage member, a floor slab, a member assembling method and a floor slab construction method. The prefabricated floor slab reinforcement cage member comprises a bottom mold and a steel reinforcement truss mounted above the bottom mold, wherein the bottom mold comprises a plurality of longitudinal support templates arranged in parallel and a plurality of transverse support templates arranged between every two adjacent longitudinal support templates; the longitudinal support templates are integrally connected with the transverse support templates on both sides; the steel reinforcement truss is formed by connecting reinforcing steel bars arranged above the longitudinal support templates with reinforcing steel bars arranged above the transverse support templates in a cross manner; the steel reinforcement truss is integrally connected with the longitudinal support templates. According to the invention, the assembly of large members and large-structure space buildings can be realized; the working procedure is simplified; the high-altitude work is reduced; the current national code for reinforced concrete reinforcement can be satisfied; the cost is reduced; the assembly efficiency, quality and positioning support precision are improved; the on-site positioning is convenient; the process is controllable.