The invention relates to a method for manufacturing a formed plate by utilizing papermaking wastes, comprising the following steps of: A. preparing cut-off dust-removing material residues, slurry residues, papermaking sludge and boil flue gas-desulphurizing gypsum by weight part, uniformly mixing, drying and then pulverizing into a powdery mixed raw material; B. preparing the powdery mixed raw material, a magnesium lignosulfonate solution or a calcium lignosulphonate solution and plant straw particles by weight part, and uniformly mixing to obtain a basic raw material of the plate; and C. placing the basic raw material of the plate in a forming mould and implanting a strip-shaped skeleton or a grid-shaped skeleton, slicking, demoulding after forming the basic raw material of the plate by the compression of a press machine, and then sizing and drying to obtain the product of the formed plate. The method comprehensively utilizes a plurality of papermaking wastes and has the advantages of simple technology, low production cost, good quality, no three-waste discharge and no environmental pollution, and the manufactured formed plate has the advantages of high adhesive strength, high mechanical properties comprising compression resistance, tensile resistance, bending resistance, impact resistance and the like, good processing performance and wide application range.