A multi-degree-of-freedom dynamic magnifier (MDOF-DM) is proposed, aiming to enhance the output performance of the piezoelectric vibration energy harvester (PVEH). By combining a simplified device model and using COMSOL Multiphysics software, the frequency response curves of the PVEH with and without the MDOF-DM were obtained, the results reflected that the MDOF-DM can enhance the electrical output of the energy harvester. Based on the simulation model, the dimensional parameters of the MDOF-DM were optimized, and the influence of these parameters on the difference between the system’s first two resonant frequencies, as well as the impact of each structural parameter on the electrical output performance of the PVEH, were investigated. Experimental frequency response results showed that when the difference between the first two resonant frequencies of the system is minimized to 90.74 Hz, the peak value of the open-circuit voltages of the piezoelectric bimorph in series reached 18.78 V and 10.26 V, respectively, which are767% and 371% higher, compared to the PVEH without the MDOF-DM. The optimized load power at the two resonant frequencies reaches 933.23 μW and 344.14 μW, respectively. The experiments demonstrate that this method can significantly enhance the output performance of PVEH.