A new type of coastal structure is proposed to reduce construction-cost and construction-space by integrating wave energy converters (WECs) into breakwater system. To develop this type of system to be more stable and effective, this paper focuses on investigating and improving an existing concept of integrated WEC type of breakwater system using a numerical method based on OpenFOAM®. Validation of the numerical setup is conducted by comparing the numerical predictions with relevant experimental data collected in a wave tank at Dalian University of Technology. The integrated WEC type of breakwater system considered in this paper is a pile-restrained WEC-type dual-floating breakwater system. The two floating breakwaters in this system are constrained to heave motion independently and work as a heaving-oscillating buoy type of WECs driven by a linear power take-off damping system (PTO system). Two parameters including wave transmission factor and capture width ratio (which is defined as the ratio of absorbed wave power to the incident wave power in the device width) are studied and discussed in the paper. The range of effective frequencies (range with wave transmission factor KT < 0.5 and capture width ratio CWR > 0.2) is obtained to evaluate the performance of this system with regard to both breakwater and WEC. These results indicate that damping coefficient of PTO system and gap width between two floating bodies influence wave transmission factor and capture width ratio, and the range of effective frequencies can be improved by the appropriate damping coefficient and gap width.