Sea tests of a floating breakwater-wave energy converter (B-WEC) system have been carried out in South China. The wave energy converter in the B-WEC system is mainly composed of an oscillating buoy, which is restricted to move along the sidewall of the moored floating breakwater, and wave power is extracted by the relative motion between the buoy and the breakwater. In this paper, the performance of the system is analyzed using analytical methods. Based on the solution of the diffraction and radiation problems, the frequency-domain hydrodynamic model has been developed using the Lagrange multiplier method. In particular, the Bragg reflection phenomenon of the floating system and its influence on the hydrodynamic performance are analyzed theoretically. It is found that: 1) the Bragg reflection occurs for both cases of large and small spacing; and 2) the presence of Bragg reflection reduces the power extraction efficiency of the system. As the spacing increases, the location of Bragg resonance shifts to the lower frequency region. From an engineering and wave energy extraction point of view, Bragg reflection shall be avoided for the floating B-WEC system.