Abstract This study investigates the waves and current field interaction with a perforated floating breakwater which is fastened by tension lags. As the predecessor done, the porous media governing equation is adopted inside the perforated floating breakwater, but a control volume concept has been applied in the breakwater in order to find the external forces on the system. A new dispersion equation has been introduced with the fact of the uniform current influence on the reflection waves (moving upstream direction) and the transmission waves (moving downstream direction). Since the whole system belongs to a domain problem and also assumes it can be linearlized, a boundary element method (BEM) is developed to solved the problem. To confirm this new BEM is correct and accuracy, a zero current has been set and compared its results with analytical solutions that was published by the predecessor. The comparison between the new BEM and analytical solutions has good agreements. It means the BEM developed by this paper has its own accuracy. Based on the same numerical model, a floating breakwater and waves/current interaction problems are investigated. The results have shown that the uniform current will degrade the reflection coefficients but increase the transmission coefficients. In general, the perforated floating breakwater, which is deeper under the water and longer in width, has smaller transmission coefficients. But practically when designing a perforated floating breakwater, we still suggest to increase the width rather than to deepen the depth. It is because the effects of dissipating wave energy are more obvious when increasing the width.