A novel testing method for the protection effect of locking device on a magnetic bearing flywheel was proposed by consideration of the performance of existing locking devices and magnetic bearing flywheels. By taking a repeated clamping locking device as an example, its protection effect for magnetic bearing flywheels was evaluated from the performance of magnetic bearing flywheel, vibration macroscopic response and microscopic wear. With comparative analysis on the performance data of the magnetic bearing flywheel and the locking device before and after environmental mechanics tests, they could run normally or not were judged. In the mechanics tests, an acceleration mechanics sensor and an eddy current displacement sensor were respectively used for measuring online response spectra of flywheel system and the vibration displacement between stator and rotor, and for evaluating the macroscopic protection function of the locking device for the flywheel. After mechanics tests, a Scanning Electron Microscopy (SEM) and an Energy Dispersive Spectroscopy (EDS) were applied to analyzing the wear morphology and the spectra of locking surface, and the microscopic protection function was obtained. This testing method provides important significance for detecting of similar aerospace products.