The invention discloses an assembled large-module welding composite beam board with a plane truss temporary support and belongs to the technical field of structural engineering. The assembled large-module welding composite beam board comprises a large-module composite beam board A and a large-module composite beam board B and is characterized in that the quadrilateral three-dimensional truss temporary support is connected with a beam through connecting plates and bolts to form a temporary integral structure; a reinforcing mesh is laid on the temporary support, the extension parts of reinforcing steel bars are welded with beam flanges, a prefabricated concrete layer is poured, and concrete is poured to the inner sides of the flanges of the beam during pouring to form an assembled large-module beam board structure; the assembled large-module composite beam board structure is prefabricated in a factory, transported to a construction site and hoisted in position, a floor upper reinforcingmesh is laid at the top of the prefabricated concrete layer according to the design, and the residual floor concrete is poured to form a composite floor; after floor curing is finished, the bolts areremoved and the temporary support is demounted to complete the construction of the assembled composite floor. The assembled large-module welding composite beam board has the advantages that hoisting weight can be reduced, and assembling precision and construction efficiency can be increased.