This paper aims to improve the off-resonance energy harvesting performance of a vibration-based energy harvesting system by exploiting the dynamic interaction between two attractive magnets. A static force-displacement model is firstly derived by a simple experiment to describe the magnetic force and then extended to the dynamic model to characterize the transient interaction of the magnets. A theoretical model is developed and experimentally verified to be capable of accurately predicting the voltage and power outputs of the proposed off-resonance energy harvesting system with different resistive loads. The performance of the proposed energy harvesting system under off-resonance excitations is examined and evaluated by comparing with the one of the system without magnetic interaction. Results reveal that the nonlinear dynamic force induced by the relative motion between the two magnets could significantly enhance the off-resonance power output. The influence of the distance between the two magnets, as well as the external resistive load, on the voltage and off-resonance power outputs of the system is studied. The proposed magnetic field enhanced energy harvesting system has 1760 times more power output than the counterpart system without magnetic interaction at the off-resonance harmonic excitation of 3 Hz and 0.5 m/s2 and an optimal resistance of 20 kΩ.