The invention provides a large rotating inertia light composite flywheel for a satellite and a preparation method thereof and relates to the technical field of composite materials. The large rotatinginertia light composite flywheel for the satellite is applied to a metal and composite material co-curing and integrally-molded composite material member and is a key technology for realizing preparation of a light large rotating inertia flywheel for the satellite. The large rotating inertia light composite flywheel for the satellite comprises metal rings, carbon fiber composite material skins, carbon fiber composite material reinforcing rings and foam ribs. A forming mold consists of combined female mold and male mold and metal ring limiting tools; a male mold consists of a steel segmented male mold block and a silicon rubber soft mold; a female mold consists of an integral concave mold and a silicon rubber soft mold block. The skins, the reinforcing rings and the ribs of the large rotating inertia light composite flywheel for the satellite adopt continuous fiber prepreg to realize the making of a prefabricated part, and then the metal rings sleeve the external side of the prefabricated part, and the co-curing and molding of the large rotating inertia light composite flywheel for the satellite are realized by using a hot pressing process. The developed large rotating inertia lightcomposite flywheel for the satellite satisfies requirements on the rigidity and the strength of reducing the weight and centrifugal force of a wheel body and also satisfies large rotating inertia equilibrium stability requirements.