This paper reports on the development of a two-dimensional, fully nonlinear CFD (Computational Fluid Dynamics) model with dynamic mesh to analyze the performance of a heave-only floating OWC (oscillating water column) device. The model was validated against previous experimental, analytical and numerical results on wave–air–structure interaction of others. The results showed that both the turbine pneumatic damping coefficient and mooring spring elasticity coefficient have a significant effect on the power capture efficiency. The heave-free floating OWC device has two resonance frequencies: natural frequency of OWC and natural frequency of chamber. The frequency band width of high efficiency can be adjusted by turbine damping coefficient and stiffness of mooring spring so as to harness more energy from marine environment with varied wave frequencies.