Abstract: Based on the hypothesis of plane stress, a method is proposed for calculating the centrifugal stress and initial ultimate rotating speed of the multi-ring intermixing composite flywheel. 2D axisymmetric FEM is used to verify the effectiveness of this method. It can provide the reference for the elementary design of the multi-ring intermixing composite flywheel. The results also show that the initial ultimate rotating speed and energy-storage density of a hollow structural flywheel are both higher than of the solid structural flywheel of whether a single material or an intermixing material. As to hollow structures, it can realize an equal-strength design through the selection of a suitable material sequence.