In this paper, the hydrodynamic performance of a floating breakwater-Wave Energy Converter (WEC) integrated system was investigated under the framework of the linear potential flow theory, with a focus on the effect of the coastal reflection. The reflection coefficient and capture width ratio were verified using the rule of wave energy flux conservation. The water wave resonances, including the piston- and sloshing-mode, between the device and the coastal wall, were excited. By comparing to the cases without the coastal wall, the presence of the coastal wall led to the significant modifications of the hydrodynamic characteristics, efficiency and wave attenuation performance of the system. Specifically, the occurrence of the piston- and sloshing-mode resonance accompanies the increment of the efficiency of the system. The null efficiency was found when the device was located at the node of standing waves, which was formed due to the presence of the coastal wall. The effect of the coastal wall in irregular waves was found to be relatively milder when compared to that in regular waves.