A flywheel rotor assembled by magnetic beas, a metal hollow hub and three composite cylindrical rings was designed for a high energy storage density magnetic suspended flywheel. The hollow hub made of high strength steel 18Ni350 was used to change the distribution of centrifugal stress, reduce the maximum radial stress and ensure that the working gap of radial magnetic bearings was a constant when the rotor rotated at a high speed. The interference between rotor rings could provide an initial pressure to prevent the rotor from delamination when the rotor rotated at a high speed. In order to find out the quantitative relationship among these factors such as the properties of high strength steel hollow hub,the thickness ratio of rings and the mathematical calculation model was proved accurately by the interference between rings, an mathematical calculation model of the stress distribution was established by a simplified stress model and the mathematical calculation model was proved accurately by the finite element method. Finally, an optimized design scheme was proposed. Obtained results show that the strength distribution can be improved and ultimate speed of the rotor can be increased when the thickness of the outermost ring or the interference between middle ring and outermost ring are increased. When the rotate speed of the rotor is up to 50 000 r/min，the total storage energy can reach 110 Wh，and the corresponding specific energy density is about 40 Wh/kg. These results give a useful hint for the design and optimization of mental-composite flywheel rotors.