To remedy the defect of an one-off locking device which can not repeat locking or releasing for a magnetic bearing flywheel, a novel repeated locking device based on the motor, extension and shrinkage mechanism was proposed and the composition and working principles of the locking device were introduced. According to the deformation of carbon fiber, the locking process of locking device was divided into stages of bending and compressing, and its mechanical property was analyzed. The software of Multidisciplinary Design Optimization (iSIGHT) combined with the finite element analysis software (ANSYS) were applied to the optimization of carbon fibers. Then,by taking the structural strength, structural force and the resonance frequency as constraints, the carbon fiber was optimized by using the method of point-by-point comparing at macrocosm combined with the sequential quadratic programming method. The result indicates that the mass of carbon fiber reaches minimum by decreasing from 112 g to 46 g (is reduced by 59%) when the number of carbon fiber slices is 12. It is concluded that the method improves the reliability and efficiency of locking device designed, and has important significance in the optimization design of flywheel systems.