The invention discloses a preparation method of a bamboo-wood orthogonal composite board. The preparation method comprises the following steps that (1) rectangular bamboo chips are dried until the water content is 9-15%, and surface sanding or planning is carried out on the rectangular bamboo chips to obtain strip-shaped bamboo chips; (2) wood sawn timber is dried until the water content is 9-15%,and the upper and lower surfaces of the wood sawn timber are planned; and (3) the strip-shaped bamboo chips and the wood sawn timber are produced into the bamboo-wood orthogonal composite board, wherein the bamboo-wood orthogonal composite board is formed by gluing and pressing a plurality of layers of bamboo chips and a plurality of layers of wood. The preparation method adopts an orthogonal bamboo-wood composite structure, the structure is stable, the performance is superior, the advantages of wood and bamboo are fully used, and an ingenious, green and environment-friendly and back to basics decoration and furniture material is simultaneously provided for the public.