<p>This study applies a double snap-through mechanism on a box-type oscillating buoy (OB) wave energy converter (WEC)-floating breakwater integrated system (OB WEC-FB) to simultaneously achieve efficient wave energy conversion and nearshore protection within a low-frequency bandwidth. This mechanism consists of four oblique springs and can operate in mono-stable, bi-stable, and tri-stable modes. A viscous-flow-based numerical model is established to investigate the hydrodynamic performance and dynamic behavior of the proposed multi-stable breakwater. The operational performance of the breakwater at different dynamic modes is first compared. The effects of the springs’ original length and stiffness coefficient are then analyzed. The results show that the tri-stable breakwater has a wider resonance frequency tuning range than the bi-stable one, both of which outperform the mono-stable and linear ones in shifting the effective bandwidth to a lower frequency range. For a tri-stable breakwater, a large distance between outermost potential wells is conducive to tuning resonance frequency, whereas shallow potential wells limit this effect. The increase in spring stiffness distinctly causes a higher potential barrier and thus constrains the motion response of the breakwater. A well-designed double snap-through mechanism can excite large-amplitude inter-well motion, tune the resonance frequency of breakwater from 3.98 to 1.96 rad/s, and decrease the lower limit of the effective transmission bandwidth from 3.75 to 3.00 rad/s. It is crucial for improving the power absorption and wave attenuation capabilities of multi-stable OB WEC-FB. This study contributes to the limited research on the implementation of a double snap-through mechanism on multifunctional marine structures. It establishes the underlying connection between nonlinear dynamic behaviors and hydrodynamic coefficients.</p>