The invention belongs to the technical field of composite autoclave forming technologies, and particularly relates to a manufacturing tool for a composite multi-beam-box-section co-cured and formed core material. The manufacturing tool comprises two core material forming molds arranged side by side. The adjacent sidelines of the core material forming molds are both of rounded corner structures. The manufacturing tool further comprises cover plates, and an area where the core material is located is defined by the cover plates and the two rounded corner structure. The invention further relates to a technology for manufacturing the core material through the manufacturing tool. According to the manufacturing tool and the manufacturing technology for the core material, on the basis of an existing technology that assembling is conducted after multiple times of curing, the part strength is improved, and the forming quality can be ensured. For the technical scheme is adopted, compared with the prior art, the manufacturing tool and the manufacturing technology have the beneficial effects that the forming strength of the joint of a part middle beam and a skin is ensured, and accordingly, the part forming quality is ensured. The manufacturing technology is easy to implement, and the repeatability is high.