The invention belongs to the technical field of composite material autoclave forming technology, and specifically relates to a composite material multi-beam box section co-curing accurate forming technology. The technology comprises the following steps: manufacturing a beam mould assembly, manufacturing a beam blank, assembling the beam mould assembly and the beam blank, manufacturing a skin mould assembly and a skin blank, assembling the beam mould assembly-the beam blank, the skin mould assembly, and the skin blank. On the basis of a conventional multiple curing and reassembling technology, one time co-curing accurate forming is realized, and the forming quality is guaranteed. The technology has the advantages that the precise positioning of an upper wallboard forming die and a lower wallboard forming die is realized; the parallel degree of the upper wallboard forming die and the lower wallboard forming die is guaranteed; the height of box sections is guaranteed; the precise positioning of beam and slab parts during the assembly and curing process is ensured; thus the thickness and axis degree of parts are ensured, the operation is simple, the manufacturing period is shortened, the manufacturing cost is reduced, and the weight is reduced.