The invention provides a low-cost simple mold of composite materials for airplanes and a fast manufacturing method. Aiming at the situation that a mold is generally integrally manufactured by metal materials, such as Q235A and Invar during molding of the composite materials for airplanes, the invention provides a special mold for manufacturing the molded surface of a thin-shell mold of composite materials for airplanes, and the fast manufacturing method. Common steel plates are manufactured into a grid frame structure, and the grid frame structure mainly consists of rib plates, a base, technological positioning holes and the like, wherein the rib plates are formed by laser cutting according to the mathematic model of composite material parts, the rib plates are connected with the base in a welding manner, the rib plates in two directions are integrated into a net shape in a welding or insertion manner, filling materials are injected in empty slots of a grid to be scrapped according to the molded surface, the mold strength is guaranteed, and heat dissipation is accelerated; the technological positioning holes are formed in the mold, so that the molded surface of the molded thin-shell mold is guaranteed to be precisely and repeatedly positioned on a numerical control machine tool, the precision is guaranteed, the mold materials are effectively saved, and the manufacturing cost of the mold is reduced.