The invention discloses a bicycle hook of a weight-reducing composite material. The bicycle hook comprises a hook body, wherein an obtuse angle end of the hook body is provided with a hook hole for being pivoted with a rear wheel to form two extension pipes with an angle; one pipe end is connected with the upper fork of the rear wheel of a frame, and the other pipe end is connected with a lower fork of the rear wheel; and the hook body is integrally formed by foaming material and carbon fiber composite material coated on the outer layer. The PU foaming material is pre-formed into an inner core of the hook; and the PU pre-formed inner core is coated by the carbon fiber composite material and heated in a cavity of a hook mould so that the PU foaming support force and an outer mould act together to form the hook. According to the invention, the PU foamed inner support and the outer mould are formed together, the yarn clip problem is prevented during the formation, the yarn layer of the carbon fiber is uniform, the weight of the entire bicycle is reduced and the reinforcing function is realized.