The invention discloses a method for manufacturing a wooden beam slab. The method comprises the following steps of: (1) pretreating a wooden single slab, namely immersing the wooden single slab into a copper sulfate solution according to a volume ratio of the wooden single slab to the copper sulfate solution of 1:6-1:7 at room temperature and normal pressure for 8-10 hours, then taking out the wooden single slab, drying the wooden single slab at the temperature of 100-110 DEG C until the moisture content of the wooden single slab is proper, and pretreating the wooden single slab; (2) assembling a blank, performing double-face sizing on the pretreated wooden single slab by an epoxy resin adhesive, wherein the sizing amount is 220-280 g/m<2>; the wooden single slab adopts a parallel blank assembling mode; a glass fiber cloth and wooden single slab blank assembling mode is used for alternately arranging the wooden single slabs, so that both the uppermost layer and the bottommost layer are provided with the wooden single slab; and (3) performing cold-pressing and forming, namely after blank assembling is finished, the wooden single slab is put into a cold press, pressurizing the cold press to 20-30 MPa, keeping the pressure for 24-36 hours, then releasing the pressure, and cutting off 8-12 cm from each edge to obtain the wooden beam slab. The method is easy to implement, convenient to operate, low in production cost and suitable for large-scale production.