Abstract: Multi-ring pressfit is one effective way of solving the problem that the radial strength of composite flywheel is too low. A simplified model about the plane stress is adopted in this paper. Considering the increase of actual misfit in the pressfit, a method of calculating the stress of the multi-ring flywheel subjected to misfit is proposed. Based on the theory of stack, an approach of calculating the stress of the multi-ring flywheel subjected to centrifugal load is advanced. To ensure the flywheel against from separation, the concept and calculation of an interrelated critical rotating speed are introduced. The results showed that the effect of deformation in the pressfit on the stress of a flywheel subjected to misfit could not be neglected, the misfit and ring number having close relation with the stress and interrelated critical rotating speed of the flywheel.