A novel magnetic bistable device (MBD) is proposed to improve the efficiency of energy harvesting of a point absorber wave energy converter (WEC) by decreasing the potential barrier of the bistable energy absorber. The novel MBD is mainly composed of two pairs of coaxial permanent magnet rings with different sizes. For the permanent magnet rings, one pair has the same magnetic field direction to provide negative stiffness and the other magnet rings have nonlinear positive stiffness property with a reverse magnetic field direction. The nonlinear dynamic model is established by adopting the state space model approach during solving the convolution integral of radiation force. The capture width ratio of the WEC with the novel MBD is studied with the change of design parameters in regular wave. Then the effect of structural parameters for the novel MBD on the wave energy capture ratio is discussed. The results indicate that using the novel MBD can significantly improve the performance of point absorber WEC especially under low wave excitations in comparison with that of the WEC with traditional MBD.