The Oscillating Wave Surge Converter (OWSC) has been widely adopted in energy extraction from sea waves in recent years, particularly in relatively shallow water areas. In this research work, the wave energy absorption efficiency of dual OWSCs with various cross-section shapes, including diamond-shaped flap, cylindrical flap, elliptical flap, and rectangular flap, were investigated using a coupled numerical model between SPH and chrono-engine. A single OWSC was also numerically examined for comparison. In addition to the comparison between a single unit and dual flap OWSCs, design parameters like the interval between the two flaps, wave conditions, the water depth, and the linear PTO damping were also examined in this work. The numerical results suggest that the rectangular flap performs better in energy extraction than the other flap shapes under most wave conditions. Besides, the distances between the two flaps significantly affect energy extraction. In addition, results further suggest that the energy performance will drop when the distance between the two flaps equals one wavelength. Furthermore, the submerged depth of the flap structure plays an important role in wave energy extraction. When the flap height is less than the water depth, the wave energy efficiency increases at the beginning and then decreases as the linear PTO damping increases. If the flap height is more than the water depth, the energy extraction performance of the dual OWSC can be significantly improved.