<p>Rotary motion energy harvesting technology has garnered significant attention for its potential to continuously power low-power electronic devices, such as wireless sensors. To address the limitation of effective energy harvesting occurring only at the resonant frequency, this study proposes an innovative magnetostrictive rotational motion energy harvester based on a shared pre-magnetized magnetic field. By magnetizing the mass block at the tip of the cantilever beam in the same direction as the pre-magnetized magnetic field, the structure achieves, for the first time, an upregulation of the system’ resonant frequency through the nonlinear magnetic force generated between them. To elucidate the influence mechanism of the nonlinear magnetic force on system performance, magnetic force distribution along various directions of the cantilever beam during motion is obtained through magnetic field simulations and curve fitting, followed by numerical simulations and comparative analysis of the harvester’s output characteristics. Results indicate that the introduction of a nonlinear magnetic force not only effectively increases the system’s resonant frequency but also mitigates the super-resonance suppression phenomenon and enhances energy output efficiency. Additionally, this study systematically investigates the effect of the number of coil turns on output performance. Experimental results show that the innovative system can expand the frequency response bandwidth by 1.28–1.83 times. Additionally, the output performance improves by up to 11.9 times when the number of coil turns is optimized to 1000. These results validate the accuracy of the theoretical model and demonstrate the potential of the proposed structure for practical applications in rotary motion.</p>