This paper presents a frequency domain method for predicting the relative wave elevation due to the hydrodynamic interaction between two floating structures in the beam waves. The strip method has been found to be a practically useful technique to analyze the hydrodynamically coupled motions of two parallel structures in waves. The two-dimensional procedure which is an integral equation method is therefore used in this paper. The present study uses the linearized resultant pressure including the interaction effect to calculate the wave elevation. Both diffraction and radiation cases are considered. The relative wave elevations at each hull are investigated and the wave elevation amplitudes along the sea surface between two structures are also analyzed. It was found that some significant waves occur at the coupled resonance of the body motion. Therefore, the water shipping must be considered as an important factor for the safety of cargo transfer problem. The results shown in the paper may be regarded as analytically reasonable from the viewpoint of energy conservation.